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Mailfromd |
General-Purpose Mail Filter |
Sergey Poznyakoff |
Dedico aquest treball a Lluis Llach, per obrir els nous horitzons.
mailfromd
sed functionmailfromd
Mailfromd Command Line Syntax
mailfromd with Various MTAs
calloutd
mfdbtool
mtasim — a testing tool
This edition of the Mailfromd Manual, last updated 11 August 2022,
documents mailfromd Version 8.14.
Mailfromd Manual: 
Simple Mail Transfer Protocol (SMTP) which is the standard
for email transmissions across the Internet was designed in the
good old days when nobody could even think of the
possibility of e-mail being abused to send tons of unsolicited
messages of dubious contents. Therefore it lacks mechanisms that
could have prevented this abuse (spamming), or at least could
have made it difficult. Attempts to introduce such mechanisms (such
as SMTP-AUTH
extension) are being made, but they are not in wide use yet and,
probably, their introduction will not be enough to stop the e-mail
abuse. Spamming is today’s grim reality and developers spend lots of
time and efforts designing new protection measures against it.
Mailfromd is one of such attempts.
The package is designed to work with any MTA supporting ‘Milter’ or ‘Pmilter’ protocol, such as ‘Sendmail’, ‘MeTA1’ or ‘Postfix’. It allows you to:
Mailfromd Manual:
mailfromd.The idea of the utility appeared in 2005, and its first version
appeared soon afterward. Back then it was a simple implementation of
Sender Address Verification (see SAV) for ‘Sendmail’ (hence
its name – mailfromd) with rudimentary tuning
possibilities.
After a short run on my mail servers, I discovered that the utility was not flexible enough. It took less than a month to implement a configuration file that allowed the user to control program and data flow during the ‘envfrom’ SMTP state. The new version, 1.0, appeared in June, 2005.
Next major release, 1.2 (1.1 contained mostly bugfixes), appeared two months later, and introduced mail sending rate control (see Rate Limit).
The program evolved during the next year, and the version 2.0 was
released in September, 2006. This version was a major change in the
main idea of the program. Configuration file become a flexible filter
script allowing the operator to control almost all SMTP states. The
program supplied in the script file was compiled into a pseudo-code at
startup, this code being subsequently evaluated each time the filter
was invoked. This caused a considerable speed-up in comparison with
the previous versions, where the run-time evaluator was traversing the
parse tree. This version also introduced (implicitly, at the time),
two separate data types for the entities declared in the script, which
also played its role in the speed improvement (in the previous
versions all data were considered strings). Lots of improvements were
made in the filter language (MFL, see MFL) itself, such
as user-defined functions, the switch statement, the catch
statement for handling run-time errors, etc. The set of
built-in functions extended considerably. A testsuite (using
DejaGNU) was introduced in this version.
During this initial development period the limitations
imposed by libmilter implementation became obvious. Finally,
I felt they were stopping further development, and decided
that mailfromd should use its own ‘Milter’
implementation. This new library, libgacopyz was the main
new feature of the 3.0 release, which was released in November, 2006.
Another major feature was the --dump-macros option and
macros to rc.mailfromd script, that were intended
to facilitate the configuration on ‘Sendmail’ side.
The development of 3.x (more properly, 3.1.x) series concentrated mainly on bug-fixes, while the main development was done on the next branch.
The version 4.0 appeared on May 12, 2007. A full
list of changes in this release is more than 500 lines long, so it is
impractical to list them here. In particular, this version introduced
lots of new features in MFL syntax and the
library of useful MFL functions. The runtime engine was
also improved, in particular, stack space become expandable which
eliminated many run-time errors. This version also provided a
foundation for MFL module system. The code generation
was re-implemented to facilitate introduction of object files in
future versions. Another new features in this release include
SPF support and mtasim utility — an MTA
simulator designed for testing mailfromd scripts
(see mtasim). The test suite in this version was made portable by
rewriting it in Autotest.
Another big leap forward was the 5.0 release, which appeared on December 26, 2008. It largely enriched a set of available functions (61 new functions were introduced, which amounts to 41% of all the available functions in 5.0 release) and introduced several improvements in the MFL itself. Among others, function aliases and optional arguments in user-defined functions were introduced in this release. The new “run operation mode” allowed to execute arbitrary MFL functions from the command line. This release also raised the Mailutils version requirements to at least 2.0.
Version 6.0, which was released in on 12 December, 2009, introduced a full-fledged modular system, akin to that of Python, and quite a few improvements to the language. such as explicit type casts, concatenation operator, static variables, etc.
Starting from version 7.0, the focus of further development of
mailfromd has shifted. While previously it had been regarded
as a mail-filtering server, since then it was developed as a system for
extending MTA functionality in the broad sense, mail
filtering being only one of features it provides.
Version 7.0 makes the MFL syntax more consistent and the language itself more powerful. For example, it is no longer necessary to use prefixes before variables to dereference them. The new ‘try--catch’ construct allows for elegant handling of exceptions and errors. User-defined exceptions provide a way for programming complex loops and recursions with non-local exits.
This version introduces a concept of dedicated callout server.
This allows mailfromd to defer verifications for a later
time if the remote server does not response within a reasonably short
period of time (see SMTP Timeouts).
Six years later the version 8.0 was released. This version was a major rewrite of the mailfromd codebase. It introduced a separate callout daemon that made it possible to separate the mailfromd server machine from machines performing callout checks. The MFL language was extended by a number of built-in functions.
Since version 8.3 (2017-11-02) mailfromd uses
‘adns’1 for
DNS queries.
The version 8.7 released in July, 2020 introduced DKIM support.
Mailfromd Manual:
Many people need to be thanked for their assistance in developing
and debugging mailfromd. After S. C. Johnson, I can say
that this program “owes much to a most stimulating collection of
users, who have goaded me beyond my inclination, and frequently beyond
my ability in their endless search for "one more feature". Their
irritating unwillingness to learn how to do things my way has usually
led to my doing things their way; most of the time, they have been right.”
A real test for a program like mailfromd cannot be done
but in conditions of production environment. A decision to try it
in these conditions is by no means an easy one, it requires courage
and good faith in the intentions and abilities of the author. To
begin with, I would like to thank my contributors for these virtues.
Jan Rafaj has intrepidly been using mailfromd since its
early releases and invested lots of efforts in improving the program
and its documentation. He is the author of many of the MFL
library functions, shipped with the package. Some of his ideas are
still waiting in my implementation queue, while new ones are
consistently arriving.
Peter Markeloff patiently tested every mailfromd
release and helped discover and fix many bugs.
Zeus Panchenko contributed many ideas and gave lots of helpful
comments. He offered invaluable help in debugging and testing
mailfromd on FreeBSD platform.
Sergey Afonin proposed many improvements and new ideas. He also invested a lot of his time in finding bugs and testing bugfixes.
John McEleney and Ben McKeegan contributed the token bucket filter implementation (see TBF).
Con Tassios helped to find and fix various bugs and contributed the
new implementation of the greylist function (see greylisting types).
The following people (in alphabetical order) provided bug reports and helpful comments for various versions of the program: Alan Dobkin, Brent Spencer, Jeff Ballard, Nacho González López, Phil Miller, Simon Christian, Thomas Lynch.
Mailfromd Manual:
mailfromdMailfromd is a general-purpose mail filtering daemon and a
suite of accompanying utilities for Sendmail2, MeTA13, Postfix4 or any other MTA that
supports Milter (or Pmilter) protocol. It is able
to filter both incoming and outgoing messages using a filter program,
written in mail filtering language (MFL). The daemon
interfaces with the MTA using Milter protocol.
The name mailfromd can be thought of as an abbreviation for
‘Mail Filtering and Runtime
Modification’ Daemon, with an ‘o’ for itself.
Historically, it stemmed from the fact that the original
implementation was a simple filter implementing the sender
address verification technique. Since then the program has changed
dramatically, and now it is actually a language translator and
run-time evaluator providing a set of built-in and library functions
for filtering electronic mail.
The first part of this manual is an overview, describing the features
mailfromd offers in general.
The second part is a tutorial, which provides an introduction for
those who have not used mailfromd previously. It moves from
topic to topic in a logical, progressive order, building on
information already explained. It offers only the principal information
needed to master basic practical usage of mailfromd, while
omitting many subtleties.
The other parts are meant to be used as a reference for those who
know mailfromd well enough, but need to look up some notions
from time to time. Each chapter presents everything that needs to be
said about a specific topic.
The manual assumes that the reader has a good knowledge of the
SMTP protocol and the mail transport system he uses
(Sendmail , Postfix or MeTA1).
Mailfromd Manual:
This manual is written using Texinfo, the GNU documentation formatting language. The same set of Texinfo source files is used to produce both the printed and online versions of the documentation. Because of this, the typographical conventions may be slightly different than in other books you may have read.
Examples you would type at the command line are preceded by the common shell primary prompt, ‘$’. The command itself is printed in this font, and the output it produces ‘in this font’, for example:
$ mailfromd --version mailfromd (mailfromd 8.14)
In the text, the command names are printed like this,
command line options are displayed in this font. Some
notions are emphasized like this, and if a point needs to be made
strongly, it is done this way. The first occurrence of
a new term is usually its definition and appears in the same
font as the previous occurrence of “definition” in this sentence.
File names are indicated like this: /path/to/ourfile.
The variable names are represented like this, keywords and
fragments of program text are written in this font.
Mailfromd Manual:
In contrast to the most existing milter filters,
mailfromd does not implement any default filtering
policies. Instead, it depends entirely on a filter script,
supplied to it by the administrator. The script, written in a
specialized and simple to use language, called MFL
(see MFL), is supposed to run a set of tests and to decide
whether the message should be accepted by the MTA or not.
To perform the tests, the script can examine the values of
Sendmail macros, use an extensive set of built-in
and library functions, and invoke user-defined functions.
Mailfromd Manual:
Sender address verification, or callout, is one of the
basic mail verification techniques, implemented by
mailfromd. It consists in probing each MX server
for the given address, until one of them gives a definite (positive or
negative) reply. Using this technique you can block a sender address
if it is not deliverable, thereby cutting off a large amount of spam.
It can also be useful to block mail for undeliverable recipients, for
example on a mail relay host that does not have a list of all the
valid recipient addresses. This prevents undeliverable junk mail from
entering the queue, so that your MTA doesn’t have to waste
resources trying to send ‘MAILER-DAEMON’ messages back.
Let’s illustrate how it works on an example:
Suppose that the user ‘<jsmith@somedomain.net>’ is trying to
send mail to one of your local users. The remote machine connects to
your MTA and issues MAIL FROM: <jsmith@somedomain.net>
command. However, your MTA does not have to take its word for it, so
it uses mailfromd to verify the sender address
validity. Mailfromd strips the domain name from the address
(‘somedomain.net’) and queries DNS about ‘MX’ records for that
domain. Suppose, it receives the following list
| 10 | relay1.somedomain.net |
| 20 | relay2.somedomain.net |
It then connects to first MX server, using SMTP
protocol, as if it were going to send a message to
‘<jsmith@somedomain.net>’. This is called sending a
probe message. If the server accepts the recipient address, the
mailfromd accepts the incoming mail. Otherwise, if the
server rejects the address, the mail is rejected as well. If the MX
server cannot be connected, mailfromd selects next server
from the list and continues this process until it finds the
answer or the list of servers is exhausted.
The probe message is like a normal mail except that no data
are ever being sent. The probe message transaction in our example
might look as follows (‘S:’ meaning messages sent by remote
MTA, ‘C:’ meaning those sent by mailfromd):
C: HELO mydomain.net S: 220 OK, nice to meet you C: MAIL FROM: <> S: 220 <>: Sender OK C: RCPT TO: <jsmith@somedomain.net> S: 220 <jsmith@remote.net>: Recipient OK C: QUIT
Probe messages are never delivered, deferred or bounced; they are always discarded.
The described method of address verification is called
a standard method throughout this document. Mailfromd
also implements a method we call strict. When using strict
method, mailfromd first resolves IP address of sender
machine to a fully qualified domain name. Then it obtains ‘MX’ records
for this machine, and then proceeds with probing as described above.
So, the difference between the two methods is in the set of ‘MX’ records that are being probed: standard method queries ‘MX’s based on the sender email domain, strict method works with ‘MX’s for the sender IP address.
Strict method allows to cut off much larger amount of spam, although it does have many drawbacks. Returning to our example above, consider the following situation: ‘<jsmith@somedomain.net>’ is a perfectly normal address, but it is being used by a spammer from some other domain, say ‘otherdomain.com’. The standard method is not able to cope with such cases, whereas the strict one is.
An alert reader will ask: what happens if mailfromd is
not able to get a definite answer from any of MX servers? Actually,
it depends entirely on how you will instruct it to act in this case,
but the general practice is to return temporary failure, which will
urge the remote party to retry sending their message later.
After receiving a definite answer, mailfromd will
cache it in its database, so that next time your MTA receives a
message from that address (or from the sender IP/email address pair,
for strict method), it will not waste its time trying to reach MX
servers again. The records remain in the cache database for a certain
time, after which they are discarded.
Mailfromd Manual:
Before deciding whether and how to use sender address verification, you should be aware of its limitations.
Both standard and strict methods suffer from the following limitations:
mailfromd options to find an optimal configuration.
Mailfromd eliminates this drawback by using a
cache database, which keeps results of the recent callouts.
mailfromd assumes it is OK. However in reality, a mail for a
remote address can bounce after the nearest MTA accepts the
recipient address.
This drawback can often be avoided by combining sender address verification with greylisting (see Greylisting).
yahoo.com’ do not
reject unknown addresses in reply to the ‘RCPT TO’ command, but report a
delivery failure in response to end of ‘DATA’ after a message is
transferred. Of course, sender address verification does not work with such
sites. However, a combination of address verification and greylisting
(see Greylisting) may be a good choice in such cases.
In addition, strict verification breaks forward mail delivery. This is obvious, since mail forwarding is based on delivering unmodified message to another location, so the sender address domain will most probably not be the same as that of the MTA doing the forwarding.
Mailfromd Manual:
Mail Sending Rate for a given identity is defined as the number of messages with this identity received within a predefined interval of time.
MFL offers a set of functions for limiting mail sending rate (see Rate limiting functions), and for controlling broader rate aspects, such as data transfer rates (see TBF).
Mailfromd Manual:
Sender Policy Framework, or SPF for short, is an
extension to SMTP protocol that allows to identify forged
identities supplied with the MAIL FROM and HELO
commands. The framework is explained in detail in RFC 4408
(http://tools.ietf.org/html/rfc4408) and on the
SPF Project Site.
Mailfromd provides a set of functions for using SPF to control mail flow. These are described in SPF Functions.
DomainKeys Identified Mail (DKIM) is an email authentication method designed to detect forged sender addresses in emails. Mailfromd supports both DKIM signing and verification. See DKIM, for a detailed description of these features.
Mailfromd also provides support for several third-party
spam-abatement programs, in particular SpamAssassin,
ClamAV, and DSPAM. These are discussed in
Interfaces to Third-Party Programs.
Mailfromd Manual:
This chapter contains a detailed list of steps you need to undertake in order to configure and build the package.
To build mailfromd you will need to have following
packages on your machine:
GNU mailutils is a general-purpose library for handling electronic mail. It is available from http://mailutils.org.
GNU adns is an advanced DNS client library. The recent version can be downloaded from http://www.chiark.greenend.org.uk/~ian/adns/adns.tar.gz. Visit http://www.gnu.org/software/adns, for more information.
Mailfromd is able to link with any flavor of
DBM supported by GNU mailutils. As of version
8.14 it will refuse to build without DBM.
By default, configure will try to
find the best implementation installed on your machine (preference is
given to Berkeley DB) and will use it. You can, however, explicitly
specify which implementation you want to use. To do so, use the
--with-dbm configure option. Its argument specifies the
type of database to use. It must be one of the types supported
by GNU mailutils. At the time of this writing, these are:
Berkeley DB (versions 2 to 6).
GNU DBM.
Kyoto Cabinet
Tokyo Cabinet
NDBM
To check what database types are supported by your version of mailutils, run the following command:
$ mailutils dbd gdbm kc tc ndbm
For backward compatibility, configure accepts the following
two options:
Same as --with-dbm=gdbm.
Same as --with-dbm=bdb.
For Sendmail users, it often makes sense to configure
mailfromd to use the same database flavor as sendmail.
The following table will help you do that. The column ‘DB type’ lists
types of DBM databases supported by mailfromd.
The column ‘confMAPDEF’ lists the value of confMAPDEF Sendmail
configuration macro corresponding to that database type. The column
‘configure option’ contains the corresponding option to configure.
| DB type | confMAPDEF | configure option |
|---|---|---|
| NDBM | -NNDBM | --with-dbm=ndbm |
| Berkeley DB | -NNEWDB | --with-dbm=bdb |
| GDBM | N/A | --with-dbm=gdbm |
mailfromd
After startup, the program drops root privileges. By default,
it switches to the privileges of user ‘mail’, group ‘mail’.
If there is no such user on your system, or you wish to use another
user account for this purpose, override it using DEFAULT_USER
environment variable. For example for mailfromd to run as
user ‘nobody’, use
./configure DEFAULT_USER=nobody
The user name can also be changed at run-time (see --user).
mailfromd and where its
filter script and data files will be located.
As usual, the default value for the installation prefix is /usr/local. If it does not suit you, specify another location using --prefix option, e.g.: ‘--prefix=/usr’.
During installation phase, the build system will install several files. These files are:
Main daemon. See mailfromd.
Default main filter script file. It is installed only if it is
not already there. Thus, if you are upgrading to a newer version of
mailfromd, your old script file will be preserved
with all your changes.
See MFL, for a description of the mail filtering language.
MFL modules. See Modules.
Documentation files.
MTA simulator program for testing mailfromd
scripts. See mtasim.
Pmilter multiplexor for MeTA1. See pmult.
It is build only if MeTA1 version ‘PreAlpha29.0’ or
newer is installed on the system. You may disable it by using the
--disable-pmilter command line option.
When testing for MeTA1 presence, configure assumes
its default location. If it is not found there, inform
configure about its actual location by using the following
option:
--enable-pmilter=prefix
where prefix stands for the MeTA1 installation prefix.
It is advisable to use the same settings for file name prefixes
as those you used when configuring mailutils. In particular,
try to use the same --sysconfdir, since it will facilitate
configuring the whole system.
Another important point is location of local state
directory, i.e. a directory where mailfromd keeps its
data files (e.g. communication socket, PID-file and database
files). By default, its full name is
localstatedir/mailfromd. You can change it by setting
DEFAULT_STATE_DIR configuration variable. This value can be
changed at run-time using the state-directory configuration
statement (see state-directory).
Milter port notation (see milter port specification).
If the socket name does not begin with a protocol or directory
separator, it is assumed to be a UNIX socket, located in the
local state directory. The default value is mailfrom, which is
equivalent to unix:localstatedir/mailfromd/mailfrom.
To alter this, use DEFAULT_SOCKET environment variable, e.g.:
./configure DEFAULT_SOCKET=inet:999@localhost
The communication socket can be changed at run time using
--port command line option (see --port) or the
listen configuration statement (see listen).
mailfromd database is considered valid. It is
described in more detail in Databases. The default value is
86400 seconds, i.e. 24 hours. It is OK for most sites. If, however,
you wish to change it, use DEFAULT_EXPIRE_INTERVAL environment
variable.
The DEFAULT_EXPIRE_RATES_INTERVAL variable sets default expiration time for mail rate database (see Rate limiting functions).
Expiration settings can be changed at run time using
database statement in the mailfromd configuration file
(see conf-database).
syslog implementation to use.
Mailfromd uses syslog for diagnostics output. The
default syslog implementation on most systems (most notably, on
GNU/Linux) uses blocking AF_UNIX SOCK_DGRAM sockets. As a
result, when an application calls syslog(), and
syslogd is not responding and the socket buffers get full,
the application will hang.
For mailfromd, as for any daemon, it is more important
that it continue to run, than that it continue to log. For this
purpose, mailfromd is shipped with a non-blocking
syslog implementation by Simon Kelley. This implementation,
instead of blocking, buffers log lines in memory. When the buffer log
overflows, some lines are lost, but the daemon continues to run. When
lines are lost, this fact is logged with a message of the form:
async_syslog overflow: 5 log entries lost
To enable this implementation, configure the package with --enable-syslog-async option, e.g.:
./configure --enable-syslog-async
Additionally, you can instruct mailfromd to use
asynchronous syslog by default. To do so, set
DEFAULT_SYSLOG_ASYNC to 1, as shown in example below:
./configure --enable-syslog-async DEFAULT_SYSLOG_ASYNC=1
You will be able to override these defaults at run-time by using the --logger command line option (see Logging and Debugging).
configure with all the desired options.
For example, the following command:
./configure DEFAULT_SOCKET=inet:999@localhost --with-berkeley-db=3
will configure the package to use Berkeley DB database, version 2, and ‘inet:999@localhost’ as the default communication socket.
At the end of its run configure will print a concise
summary of its configuration settings. It looks like that (with the
long lines being split for readability):
*******************************************************************
Mailfromd configured with the following settings:
Mailutils version......................... 3.15
External preprocessor..................... /usr/bin/m4 -s
DBM version............................... Berkeley DB v. 3
Default user.............................. mail
State directory...........................
$(localstatedir)/$(PACKAGE)
Socket.................................... mailfrom
Expiration interval....................... 86400
Compile asynchronous syslog............... no
Readline (for mtasim)..................... yes
Documentation rendition type.............. PROOF
Enable pmilter support.................... no
Enable GeoIP support...................... no
Enable GeoIP2 support..................... no
Enable DSPAM support...................... no
Enable DKIM support....................... yes
IPv6 support.............................. yes
*******************************************************************
Make sure these settings satisfy your needs. If they do not, reconfigure the package with the right options.
make.
make install.
Mailfromd Manual:
This chapter contains a tutorial introduction, guiding you
through various mailfromd configurations, starting from the
simplest ones and proceeding up to more advanced forms. It omits
most complicated details, concentrating mainly on the
common practical tasks.
If you are familiar to mailfromd, you can skip this
chapter and go directly to the next one (see MFL), which contains
detailed discussion of the mail filtering language and
mailfromd interaction with the Mail Transport Agent.
Mailfromd Manual:
The mailfromd utility runs as a standalone daemon
program and listens on a predefined communication channel for requests
from the Mail Transfer Agent (MTA, for short). When
processing each message, the MTA installs communication with
mailfromd, and goes through several states, collecting the
necessary data from the sender. At each state it sends the relevant
information to mailfromd, and waits for it to reply. The
mailfromd filter receives the message data through
Sendmail macros and runs a handler program
defined for the given state. The result of this run is a response
code, that it returns to the MTA. The following response
codes are defined:
continueContinue message processing.
acceptAccept this message for delivery. After receiving this code the
MTA continues processing this message without
further consulting mailfromd filter.
rejectReject this message. The message processing stops at this stage, and the
sender receives the reject reply (‘5xx’ reply code). No
further mailfromd handlers are called for this message.
discardSilently discard the message. This means that MTA will
continue processing this message as if it were going to deliver it,
but will discard it after receiving. No further interaction with
mailfromd occurs.
tempfailTemporarily reject the message. The message processing stops at this
stage, and the sender receives the ‘temporary failure’ reply
(‘4xx’ reply code). No further mailfromd
handlers are called for this message.
The instructions on how to process the message are supplied to
mailfromd in its filter script file. It is normally
called /usr/local/etc/mailfromd.mf (but can be located
elsewhere, see Invocation) and contains a set of milter
state handlers, or subroutines to be executed in various
SMTP states. Each interaction state can
be supplied its own handling procedure. A missing procedure implies
continue response code.
The filter script can define up to nine milter state handlers,
called after the names of milter states: ‘connect’, ‘helo’,
‘envfrom’, ‘envrcpt’, ‘data’, ‘header’, ‘eoh’,
‘body’, and ‘eom’. The ‘data’ handler is invoked only
if MTA uses Milter protocol version 3 or later. Two special
handlers are available for initialization and clean-up purposes:
‘begin’ is called before the processing starts, and ‘end’ is
called after it is finished. The diagram below shows the control flow
when processing an SMTP transaction. Lines marked with
C: show SMTP commands issued by the remote machine (the
client), those marked with ‘⇒’ show called handlers
with their arguments. An ‘[R]’ appearing at the start of a line
indicates that this part of the transaction can be repeated any number
of times:
⇒ begin()
⇒ connect(hostname, family, port, ‘IP address’)
C: HELO domain
helo(domain)
for each message transaction
do
C: MAIL FROM sender
⇒ envfrom(sender)
[R] C: RCPT TO recipient
⇒ envrcpt(recipient)
C: DATA
⇒ data()
[R] C: header: value
⇒ header(header, value)
C:
⇒ eoh()
[R] C: body-line
⇒ /* Collect lines into blocks blk of
⇒ * at most len bytes and for each
⇒ * such block call:
⇒ */
⇒ body(blk, len)
C: .
⇒ eom()
done
⇒ end()
Figure 3.1: Mailfromd Control Flow
This control flow is maintained for as long as each called handler
returns continue (see Actions). Otherwise, if
any handler returns accept or discard, the message
processing continues, but no other handler is called. In the case
of accept, the MTA will accept the message for
delivery, in the case of discard it will silently discard it.
If any of the handlers returns reject or tempfail, the
result depends on the handler. If this code is returned by
envrcpt handler, it causes this particular recipient address to
be rejected. When returned by any other handler,
it causes the whole message will be rejected.
The reject and tempfail actions executed by
helo handler do not take effect immediately. Instead, their
action is deferred until the next SMTP command from the
client, which is usually MAIL FROM.
Mailfromd Manual:
The mailfromd script file contains a
series of declarations of the handler procedures. Each
declaration has the form:
prog name do … done
where prog, do and done are the keywords,
and name is the state name for this handler. The dots in the
above example represent the actual code, or a set of
commands, instructing mailfromd how to process the message.
For example, the declaration:
prog envfrom do accept done
installs a handler for ‘envfrom’ state, which always approves the
message for delivery, without any further interaction with
mailfromd.
The word accept in the above example is an action.
Action is a special language statement that instructs the
run-time engine to stop execution of the program and to return a
response code to the Sendmail. There are five actions, one
for each response code: continue, accept, reject,
discard, and tempfail. Among these, reject and
discard can optionally take one to three arguments. There are
two ways of supplying the arguments.
In the first form, called literal or traditional notation,
the arguments are supplied as additional words after the action name,
separated by whitespace. The first argument is a three-digit
RFC 2821 reply code. It must begin with ‘5’ for
reject and with ‘4’ for tempfail. If two arguments
are supplied, the second argument must be either an extended
reply code (RFC 1893/2034) or a textual string to be
returned along with the SMTP reply. Finally, if all three
arguments are supplied, then the second one must be an extended reply
code and the third one must supply the textual string. The following
examples illustrate all possible ways of using the reject
statement in literal notation:
reject reject 503 reject 503 5.0.0 reject 503 "Need HELO command" reject 503 5.0.0 "Need HELO command"
Please note the quotes around the textual string.
Another form for these action is called functional notation, because it resembles the function syntax. When used in this form, the action word is followed by a parenthesized group of exactly three arguments, separated by commas. The meaning and ordering of the argument is the same as in literal form. Any of three arguments may be absent, in which case it will be replaced by the default value. To illustrate this, here are the statements from the previous example, written in functional notation:
reject(,,) reject(503,,) reject(503, 5.0.0) reject(503,, "Need HELO command") reject(503, 5.0.0, "Need HELO command")
Mailfromd Manual:
Programs consisting of a single action are rarely useful. In most cases you will want to do some checking and decide whether to process the message depending on its result. For example, if you do not want to accept messages from the address ‘<badguy@some.net>’, you could write the following program:
prog envfrom
do
if $f = "badguy@some.net"
reject
else
accept
fi
done
This example illustrates several important concepts. First or
all, $f in the third line is a Sendmail macro
reference. Sendmail macros are referenced the same way as in
sendmail.cf, with the only difference that curly braces around
macro names are optional, even if the name consists of several
letters. The value of a macro reference is always a string.
The equality operator (‘=’) compares its left and right
arguments and evaluates to true if the two strings are exactly the
same, or to false otherwise. Apart from equality, you can use the
regular relational operators: ‘!=’, ‘>’, ‘>=’, ‘<’
and ‘<=’. Notice that string comparison in mailfromd
is always case sensitive. To do case-insensitive comparison,
translate both operands to upper or lower case (See tolower, and
see toupper).
The if statement decides what actions to execute depending
on the value its condition evaluates to. Its usual form is:
if expression then-body [else else-body] fi
The then-body is executed if the expression evaluates to
true (i.e. to any non-zero value). The optional
else-body is executed if the expression yields
false (i.e. zero). Both then-body and else-body can contain
other if statements, their nesting depth is not limited. To
facilitate writing complex conditional statements, the elif
keyword can be used to introduce alternative conditions, for example:
prog envfrom
do
if $f = "badguy@some.net"
reject
elif $f = "other@domain.com"
tempfail 470 "Please try again later"
else
accept
fi
done
See switch, for more elaborate forms of conditional branching.
Mailfromd Manual:
As any programming language, MFL supports a concept of function, i.e. a body of code that is assigned a unique name and can be invoked elsewhere as many times as needed.
All functions have a definition that introduces types and names of the formal parameters and the result type, if the function is to return a meaningful value (function definitions in MFL are discussed in detail in see User-Defined Functions).
A function is invoked using a special construct, a function call:
name (arg-list)
where name is the function name, and arg-list is a comma-separated list of expressions. Each expression in arg-list is evaluated, and its type is compared with that of the corresponding formal argument. If the types differ, the expression is converted to the formal argument type. Finally, a copy of its value is passed to the function as a corresponding argument. The order in which the expressions are evaluated is not defined. The compiler checks that the number of elements in arg-list match the number of mandatory arguments for function name.
If the function does not deliver a result, it should only be called as a statement.
Functions may be recursive, even mutually recursive.
Mailfromd comes with a rich set of predefined functions
for various purposes. There are two basic function classes:
built-in functions, that are implemented by the MFL
runtime environment in mailfromd, and library
functions, that are implemented in MFL. The built-in
functions are always available and no preparatory work is needed before
calling them. In contrast, the library functions are defined in
modules, special MFL source files that contain functions
designed for a particular task. In order to access a library
function, you must first require a module it is defined in.
This is done using require statement. For example, the
function hostname looks up in the DNS the name
corresponding to the IP address specified as its argument. This
function is defined in module dns.mf, so before calling it you
must require this module:
require dns
The require statement takes a single argument: the name of the
requested module (without the ‘.mf’ suffix). It looks up the
module on disk and loads it if it is available.
For more information about the module system See Modules.
Mailfromd Manual:
Site administrators often do not wish to accept mail from hosts that
do not have a proper reverse delegation in the Domain Name System.
In the previous section we introduced the library function
hostname, that looks up in the DNS the name corresponding to
the IP address specified as its argument. If there is no
corresponding name, the function returns its argument unchanged. This
can be used to test if the IP was resolved, as illustrated in the
example below:
require 'dns'
prog envfrom
do
if hostname($client_addr) = $client_addr
reject
fi
done
The #require dns statement loads the module dns.mf,
after which the definition of hostname becomes available.
A similar function, resolve, which resolves the symbolic
name to the corresponding IP address is provided in the same
dns.mf module.
Mailfromd Manual:
A special language construct is provided for verification of sender addresses (callout):
on poll $f do when success: accept when not_found or failure: reject 550 5.1.0 "Sender validity not confirmed" when temp_failure: tempfail 450 4.1.0 "Try again later" done
The on poll construct runs standard verification
(see standard verification) for the email address specified as its
argument (in the example above it is the value of the Sendmail macro
‘$f’). The check can result in the following conditions:
successThe address exists.
not_foundThe address does not exist.
failureSome error of permanent nature occurred during the check. The existence of the address cannot be verified.
temp_failureSome temporary failure occurred during the check. The existence of the address cannot be verified at the moment.
The when branches of the on poll statement
introduce statements, that are executed depending on the actual
return condition. If any condition occurs that is not handled within
the on block, the run-time evaluator will signal an
exception5 and return temporary
failure, therefore it is advisable to always handle all four
conditions. In fact, the condition handling shown in the above
example is preferable for most normal configurations: the mail is
accepted if the sender address is proved to exist and rejected
otherwise. If a temporary failure occurs, the remote party is urged
to retry the transaction some time later.
The poll statement itself has a number of options that
control the type of the verification. These are discussed in detail
in poll.
It is worth noticing that there is one special email address which is always available on any host, it is the null address ‘<>’ used in error reporting. It is of no use verifying its existence:
prog envfrom
do
if $f == ""
accept
else
on poll $f do
when success:
accept
when not_found or failure:
reject 550 5.1.0 "Sender validity not confirmed"
when temp_failure:
tempfail 450 4.1.0 "Try again later"
done
fi
done
Mailfromd Manual:
When using polling functions, it is important to take into account possible delays, which can occur in SMTP transactions. Such delays may be due to low network bandwidth or high load on the remote server. Some sites impose them willingly, as a spam-fighting measure.
Ideally the callout verification should use the timeout values defined in the RFC 2822, but this is impossible in practice, because it would cause a timeout escalation, which consists in propagating delays encountered in a callout SMTP session back to the remote client whose session initiated the callout.
Consider, for example, the following scenario. An MFL script performs a callout on ‘envfrom’ stage. The remote server is overloaded and delays heavily in responding, so that the initial response arrives 3 minutes after establishing the connection, and processing the ‘EHLO’ command takes another 3 minutes. These delays are OK according to the RFC, which imposes a 5 minute limit for each stage, but while waiting for the remote reply our SMTP server remains in the ‘envfrom’ state with the client waiting for a response to its ‘MAIL’ command more than 6 minutes, which is intolerable, because of the same 5 minute limit. Thus, the client will almost certainly break the session.
To avoid this, mailfromd uses a special instance, called
callout server, which is responsible for running callout
SMTP sessions asynchronously. The usual sender verification
is performed using so-called soft timeout values, which
are set to values short enough to not disturb the incoming session
(e.g. a timeout for ‘HELO’ response is 3 seconds, instead of 5
minutes). If this verification yields a definite answer, that answer
is stored in the cache database and returned to the calling procedure
immediately. If, however, the verification is aborted due to a timeout,
the caller procedure is returned an ‘e_temp_failure’ exception, and
the callout is scheduled for processing by a callout server. This
exception normally causes the milter session to return a temporary
error to the sender, urging it to retry the connection later.
In the meantime, the callout server runs the sender verification again using another set of timeouts, called hard timeouts, which are normally much longer than ‘soft’ ones (they default to the values required by RFC 2822). If it gets a definitive result (e.g. ‘email found’ or ‘email not found’), the server stores it in the cache database. If the callout ends due to a timeout, a ‘not_found’ result is stored in the database.
Some time later, the remote server retries the delivery, and the
mailfromd script is run again. This time, the callout
function will immediately obtain the already cached result from the
database and proceed accordingly. If the callout server has not
finished the request by the time the sender retries the connection,
the latter is again returned a temporary error, and the process
continues until the callout is finished.
Usually, callout server is just another instance of
mailfromd itself, which is started automatically to
perform scheduled SMTP callouts. It is also possible to set up
a separate callout server on another machine. This is discussed in
calloutd.
For a detailed information about callout timeouts and their configuration, see conf-timeout.
For a description of how to configure mailfromd to use callout
servers, see conf-server.
Mailfromd Manual:
An envfrom program consisting only of the on poll
statement will work smoothly for incoming mails, but will create
infinite loops for outgoing mails. This is because upon sending an outgoing
message mailfromd will start the verification procedure, which
will initiate an SMTP transaction with the same mail server
that runs it. This transaction will in turn trigger execution of
on poll statement, etc. ad infinitum. To avoid this, any
properly written filter script should not run the verification
procedure on the email addresses in those domains that are relayed by
the server it runs on. This can be achieved using relayed
function. The function returns true if its argument is
contained in one of the predefined domain list files. These
files correspond to Sendmail plain text files used in
F class definition forms (see Sendmail Installation and
Operation Guide, chapter 5.3), i.e. they contain one domain name per
line, with empty lines and lines started with ‘#’ being ignored.
The domain files consulted by relayed function are defined
in the relayed-domain-file configuration file statement
(see relayed-domain-file):
relayed-domain-file (/etc/mail/local-host-names,
/etc/mail/relay-domains);
or:
relayed-domain-file /etc/mail/local-host-names; relayed-domain-file /etc/mail/relay-domains;
The above example declares two domain list files, most commonly
used in Sendmail installations to keep hostnames of the server
6 and names of the domains, relayed by this
server7.
Given all this, we can improve our filter program:
require 'dns'
prog envfrom
do
if $f == ""
accept
elif relayed(hostname(${client_addr}))
accept
else
on poll $f do
when success:
accept
when not_found or failure:
reject 550 5.1.0 "Sender validity not confirmed"
when temp_failure:
tempfail 450 4.1.0 "Try again later"
done
fi
done
If you feel that your Sendmail’s relayed domains are not restrictive
enough for mailfromd filters (for example you are relaying
mails from some third-party servers), you can use a database of
trusted mail server addresses. If the number of such servers is small
enough, a single ‘or’ statement can be used, e.g.:
elif ${client_addr} = "10.10.10.1"
or ${client_addr} = "192.168.11.7"
accept
…
otherwise, if the servers’ IP addresses fall within one or
several CIDRs, you can use the match_cidr function
(see Internet address manipulation functions), e.g.:
elif match_cidr (${client_addr}, "199.232.0.0/16")
accept
…
or combine both methods. Finally, you can keep a DBM
database of relayed addresses and use dbmap or dbget
function for checking (see Database functions).
elif dbmap("%__statedir__/relay.db", ${client_addr})
accept
…
Mailfromd Manual:
Some of the mail filtering conditions may depend on the value of
helo domain name, i.e. the argument to the SMTP EHLO (or
HELO) command. If you ever need such conditions, take into
account the following caveats. Firstly, although Sendmail
passes the helo domain in $s macro, it does not do this
consistently. In fact, the $s macro is available only to
the helo handler, all other handlers won’t see it, no matter what
the value of the corresponding Milter.macros.handler
statement. So, if you wish to access its value from any
handler, other than helo, you will have to store it in a
variable in the helo handler and then use this variable
value in the other handler. This approach is also recommended for
another MTAs. This brings us to the concept of
variables in mailfromd scripts.
A variable is declared using the following syntax:
type name
where variable is the variable name and type is ‘string’, if the variable is to hold a string value, and ‘number’, if it is supposed to have a numeric value.
A variable is assigned a value using the set statement:
set name expr
where expr is any valid MFL expression.
The set statement can occur within handler or function
declarations as well as outside of them.
There are two kinds of Mailfromd variables: global
variables, that are visible to all handlers and functions, and
automatic variables, that are available only within the handler
or function where they are declared. For our purpose we need a global
variable (See Variable classes, for detailed descriptions
of both kinds of variables).
The following example illustrates an approach that allows to use
the HELO domain name in any handler:
# Declare the helohost variable string helohost prog helo do # Save the host name for further use set helohost $s done prog envfrom do # Reject hosts claiming to be localhost if helohost = "localhost" reject 570 "Please specify real host name" fi done
Notice, that for this approach to work, your MTA
must export the ‘s’ macro (e.g., in case of Sendmail, the
Milter.macros.helo statement in the sendmail.cf file must contain
‘s’. see Sendmail). This requirement can be removed by
using the handler argument of helo. Each
mailfromd handler is given one or several arguments. The
exact number of arguments and their meaning are handler-specific and are
described in Handlers, and Figure 3.1.
The arguments are referenced by their ordinal number, using the notation
$n. The helo handler takes one argument, whose
value is the helo domain. Using this information, the helo
handler from the example above can be rewritten as follows:
prog helo
do
# Save the host name for further use
set helohost $1
done
Mailfromd Manual:
In previous section we have used a global variable to hold certain
information and share it between handlers. In the majority of cases,
such information is session specific, and becomes invalid if the
remote party issues the SMTP RSET command. Therefore,
mailfromd clears all global variables when it receives a
Milter ‘abort’ request, which is normally generated by this
command.
However, you may need some variables that retain their values
even across SMTP session resets. In mailfromd terminology
such variables are called precious. Precious variables are
declared by prefixing their declaration with the keyword
precious. Consider, for example, this snippet of code:
precious number rcpt_counter prog envrcpt do set rcpt_counter rcpt_counter + 1 done
Here, the variable ‘rcpt_counter’ is declared as precious and
its value is incremented each time the ‘envrcpt’ handler is
called. This way, ‘rcpt_counter’ will keep the total number of
SMTP RCPT commands issued during the session, no matter how
many times it was restarted using the RSET command.
Mailfromd Manual:
Any MTA provides a way to limit the number of recipients
per message. For example, in Sendmail you may use the
MaxRecipientsPerMessage option8. However, such methods are not flexible, so
you are often better off using mailfromd for this purpose.
Mailfromd keeps the number of recipients collected so far
in variable rcpt_count, which can be controlled in
envrcpt handler as shown in the example below:
prog envrcpt
do
if rcpt_count > 10
reject 550 5.7.1 "Too many recipients"
fi
done
This filter will accept no more than 10 recipients per message. You may achieve finer granularity by using additional conditions. For example, the following code will allow any number of recipients if the mail is coming from a domain relayed by the server, while limiting it to 10 for incoming mail from other domains:
prog envrcpt
do
if not relayed(hostname($client_addr)) and rcpt_count > 10
reject 550 5.7.1 "Too many recipients"
fi
done
There are three important features to notice in the above code.
First of all, it introduces two boolean operators:
and, which evaluates to true only if both
left-side and right-side expressions are true, and not,
which reverses the value of its argument.
Secondly, the scope of an operation is determined by its
precedence, or binding strength. Not binds more
tightly than and, so its scope is limited by the next
expression between it and and. Using parentheses to underline the
operator scoping, the above if condition can be rewritten as
follows:
if (not (relayed(hostname($client_addr)))) and (%rcpt_count > 10)
Finally, it is important to notice that all boolean expressions
are computed using shortcut evaluation. To understand what it
is, let’s consider the following expression: x and
y. Its value is true only if both x and y
are true. Now suppose that we evaluate the expression from
left to right and we find that x is false. This means that
no matter what the value of y is, the resulting expression will be
false, therefore there is no need to compute y at all.
So, the boolean shortcut evaluation works as follows:
x and yIf x ⇒ , do not evaluate y and
return falsefalse.
x or yIf x ⇒ , do not evaluate y and
return truetrue.
Thus, in the expression not relayed(hostname($client_addr)) and
rcpt_count > 10, the value of the rcpt_count variable will be
compared with ‘10’ only if the relayed function yielded
false.
To further enhance our sample filter, you may wish to make the
reject output more informative, to let the sender know what
the recipient limit is. To do so, you can use the concatenation
operator ‘.’ (a dot):
set max_rcpt 10
prog envrcpt
do
if not relayed(hostname($client_addr)) and rcpt_count > 10
reject 550 5.7.1 "Too many recipients, max=" . max_rcpt
fi
done
When evaluating the third argument to reject,
mailfromd will first convert max_rcpt to string and
then concatenate both strings together, producing string ‘Too many
recipients, max=10’.
Mailfromd Manual:
We have introduced the notion of mail sending rate in Rate Limit. Mailfromd keeps the computed rates in the special
rate database (see Databases). Each record in this
database consists of a key, for which the rate is computed, and
the rate value, in form of a double precision floating point number,
representing average number of messages per second sent by this
key within the last sampling interval. In the simplest case,
the sender email address can be used as a key, however we recommend
to use a conjunction email-sender_ip instead, so the
actual email owner won’t be blocked by actions of some spammer
abusing his/her address.
Two functions are provided to control and update sending rates. The
rateok function takes three mandatory arguments:
bool rateok(string key, number interval, number threshold)
The key meaning is described above. The interval is the
sampling interval, or the number of seconds to which the actual
sending rate value is converted. Remember that it is stored
internally as a floating point number, and thus cannot be directly
used in mailfromd filters, which operate only on integer
numbers. To use the rate value, it is first converted to messages per
given interval, which is an integer number. For example, the rate
0.138888 brought to 1-hour interval gives 500
(messages per hour).
When the rateok function is called, it recomputes
rate record for the given key. If the new rate value converted
to messages per given interval is less than threshold,
the function updates the database and returns True. Otherwise it
returns False and does not update the database.
This function must be required prior to use, by placing the following statement somewhere at the beginning of your script:
require rateok
For example, the following code limits the mail sending rate for each ‘email address’-‘IP’ combination to 180 per hour. If the actual rate value exceeds this limit, the sender is returned a temporary failure response:
require rateok
prog envfrom
do
if not rateok($f . "-" . ${client_addr}, 3600, 180)
tempfail 450 4.7.0 "Mail sending rate exceeded. Try again later"
fi
done
Notice argument concatenation, used to produce the key.
It is often inconvenient to specify intervals in seconds,
therefore a special interval function is provided. It
converts its argument, which is a textual string representing time
interval in English, to the corresponding number of seconds. Using
this function, the function invocation would be:
rateok($f . "-" . ${client_addr}, interval("1 hour"), 180)
The interval function is described in interval, and time
intervals are discussed in time interval specification.
The rateok function begins computing the rate
as soon as it has collected enough data. By default, it needs at least
four mails. Since this may lead to a big number of false positives
(i.e. overestimated rates) at the beginning of sampling interval,
there is a way to specify a minimum number of samples rateok
must collect before starting to actually compute rates. This number of
samples is given as the optional fourth argument to the function. For
example, the following call will always return True for the
first 10 mails, no matter what the actual rate:
rateok($f . "-" . ${client_addr}, interval("1 hour"), 180, 10)
The tbf_rate function allows to exercise more control over
the mail rates. This function implements a token bucket filter
(TBF) algorithm.
The token bucket controls when the data can be transmitted based on the presence of abstract entities called tokens in a container called bucket. Each token represents some amount of data. The algorithm works as follows:
This algorithm allows to keep the data traffic at a constant rate t with bursts of up to m data items. Such bursts occur when no data was being arrived for m*t or more microseconds.
Mailfromd keeps buckets in a database ‘tbf’. Each
bucket is identified by a unique key. The tbf_rate
function is defined as follows:
bool tbf_rate(string key, number n, number t, number m)
The key identifies the bucket to operate upon. The rest of
arguments is described above. The tbf_rate function returns
‘True’ if the algorithm allows to accept the data and
‘False’ otherwise.
Depending on how the actual arguments are selected the tbf_rate
function can be used to control various types of flow rates. For
example, to control mail sending rate, assign the arguments as
follows: n to the number of mails and t to the control
interval in microseconds:
prog envfrom
do
if not tbf_rate($f . "-" . $client_addr, 1, 10000000, 20)
tempfail 450 4.7.0 "Mail sending rate exceeded. Try again later"
fi
done
The example above permits to send at most one mail each 10 seconds. The burst size is set to 20.
Another use for the tbf_rate function is to limit the total
delivered mail size per given interval of time. To do so, the
function must be used in prog eom handler, because it is the
only handler where the entire size of the message is known. The
n argument must contain the number of bytes in the email (or
email bytes * number of recipients), and the t must be set to
the number of bytes per microsecond a given user is allowed to send. The
m argument must be large enough to accommodate a couple of
large emails. E.g.:
prog eom
do
if not tbf_rate("$f-$client_addr",
message_size(current_message()),
10240*1000000, # At most 10 kb/sec
10*1024*1024)
tempfail 450 4.7.0 "Data sending rate exceeded. Try again later"
fi
done
See Rate limiting functions, for more information about
rateok and tbf_rate functions.
Mailfromd Manual:
Greylisting is a simple method of defending against the spam
proposed by Evan Harris. In few words, it consists in recording the
‘sender IP’-‘sender email’-‘recipient email’ triplet of
mail transactions. Each time the unknown triplet is seen, the
corresponding message is rejected with the tempfail code. If the
mail is legitimate, this will make the originating server retry
the delivery later, until the destination eventually accepts it. If,
however, the mail is a spam, it will probably never be retried, so
the users will not be bothered by it. Even if the spammer will retry
the delivery, the greylisting period will give spam-detection
systems, such as DNSBLs, enough time to detect and blacklist it,
so by the time the destination host starts accepting emails from this
triplet, it will already be blocked by other means.
You will find the detailed description of the method in The Next Step in the Spam Control War: Greylisting, the original whitepaper by Evan Harris.
The mailfromd implementation of greylisting is based on
greylist function. The function takes two arguments:
the key, identifying the greylisting triplet, and the
interval. The function looks up the key in the greylisting
database. If such a key is not found, a new entry is created for it
and the function returns true. If the key is
found, greylist returns false, if it was inserted to the
database more than interval seconds ago, and true otherwise.
In other words, from the point of view of the greylisting algorithm, the
function returns true when the message delivery should be
blocked. Thus, the simplest implementation of the algorithm would be:
prog envrcpt
do
if greylist("${client_addr}-$f-${rcpt_addr}", interval("1 hour"))
tempfail 451 4.7.1 "You are greylisted"
fi
done
However, the message returned by this example, is not informative
enough. In particular, it does not tell when the message will be
accepted. To help you produce more informative messages, greylist
function stores the number of seconds left to the end of the
greylisting period in the global variable
greylist_seconds_left, so the above example could be enhanced
as follows:
prog envrcpt
do
set gltime interval("1 hour")
if greylist("${client_addr}-$f-${rcpt_addr}", gltime)
if greylist_seconds_left = gltime
tempfail 451 4.7.1
"You are greylisted for %gltime seconds"
else
tempfail 451 4.7.1
"Still greylisted for %greylist_seconds_left seconds"
fi
fi
done
In real life you will have to avoid greylisting some messages, in particular those coming from the ‘<>’ address and from the IP addresses in your relayed domain. It can easily be done using the techniques described in previous sections and is left as an exercise to the reader.
Mailfromd provides two implementations of greylisting
primitives, which differ in the information stored in the database.
The one described above is called traditional. It keeps in the
database the time when the greylisting was activated for the given
key, so the greylisting function uses its second argument
(interval) and the current timestamp to decide whether the key
is still greylisted.
The second implementation is called by the name of its inventor
Con Tassios. This implementation stores in the database the
time when the greylisting period is set to expire, computed by the
greylist when it is first called for the given key, using the
formula ‘current_timestamp + interval’. Subsequent calls to
greylist compare the current timestamp with the one stored in
the database and ignore their second argument. This implementation is
enabled by one of the following pragmas:
#pragma greylist con-tassios
or
#pragma greylist ct
When Con Tassios implementation is used, yet another function
becomes available. The function is_greylisted
(see is_greylisted) returns
‘True’ if its argument is greylisted and ‘False’ otherwise.
It can be used to check for the greylisting status without actually
updating the database:
if is_greylisted("${client_addr}-$f-${rcpt_addr}")
…
fi
One special case is whitelisting, which is often used
together with greylisting. To implement it, mailfromd
provides the function dbmap, which takes two mandatory arguments:
dbmap(file, key) (it also allows an optional third
argument, see dbmap, for more information on it). The first argument is
the name of the DBM file where to search for the key, the second one
is the key to be searched. Assuming you keep your whitelist database
in file /var/run/whitelist.db, a more practical example will be:
prog envrcpt
do
set gltime interval("1 hour")
if not ($f = "" or relayed(hostname(${client_addr}))
or dbmap("/var/run/whitelist.db", ${client_addr}))
if greylist("${client_addr}-$f-${rcpt_addr}", gltime)
if greylist_seconds_left = gltime
tempfail 451 4.7.1
"You are greylisted for %gltime seconds"
else
tempfail 451 4.7.1
"Still greylisted for %greylist_seconds_left seconds"
fi
fi
fi
done
Mailfromd Manual:
In your filter script you may need to verify if the given
user name is served by your mail server, in other words, to verify if
it represents a local account. Notice that in this context, the word
local does not necessarily mean that the account is local for
the server running mailfromd, it simply means any account
whose mailbox is served by the mail servers using mailfromd.
The validuser function may be used for this purpose. It
takes one argument, the user name, and returns true if
this name corresponds to a local account. To verify this, the
function relies on libmuauth, a powerful authentication
library shipped with GNU mailutils. More precisely, it
invokes a list of authorization functions. Each function is
responsible for looking up the user name in a particular source of
information, such as system passwd database, an SQL database,
etc. The search is terminated when one of the functions finds
the name in question or the list is exhausted. In the former case, the
account is local, in the latter it is not. This concept is
discussed in detail in see Authorization and Authentication Principles in GNU Mailutils
Manual). Here we will give only some practical advices for
implementing it in mailfromd filters.
The actual list of available authorization modules depends on your
mailutils installation. Usually it includes, apart from
traditional UNIX passwd database, the functions for verifying
PAM, RADIUS and SQL database accounts.
Each of the authorization methods is configured using special
configuration file statements. For the description of the Mailutils
configuration files, See Mailutils Configuration File in GNU Mailutils Manual.
You can obtain the template for mailfromd configuration by
running mailfromd --config-help.
For example, the following mailfromd.conf file:
auth {
authorization pam:system;
}
pam {
service mailfromd;
}
sets up the authorization using PAM and system passwd database. The name of PAM service to use is ‘mailfromd’.
The function validuser is often used together with
dbmap, as in the example below:
#pragma dbprop /etc/mail/aliases.db null
if dbmap("/etc/mail/aliases.db", localpart($rcpt_addr))
and validuser(localpart($rcpt_addr))
…
fi
For more information about dbmap function, see dbmap.
For a description of dbprop pragma, see Database functions.
Mailfromd Manual:
Some mailfromd functions use DBM databases to save their
persistent state data. Each database has a unique identifier,
and is assigned several pieces of information for its maintenance: the
database file name and the expiration period, i.e. the
time after which a record is considered expired.
To obtain the list of available databases along with their preconfigured settings, run mailfromd --show-defaults. You will see an output similar to this:
version: 8.14 script file: /etc/mailfromd.mf preprocessor: /usr/bin/m4 -s user: mail statedir: /var/run/mailfromd socket: unix:/var/run/mailfromd/mailfrom pidfile: /var/run/mailfromd/mailfromd.pid default syslog: blocking supported databases: gdbm, bdb default database type: bdb optional features: GeoIP greylist database: /var/run/mailfromd/greylist.db greylist expiration: 86400 tbf database: /var/run/mailfromd/tbf.db tbf expiration: 86400 rate database: /var/run/mailfromd/rates.db rate expiration: 86400 cache database: /var/run/mailfromd/mailfromd.db cache positive expiration: 86400 cache negative expiration: 43200
The text below ‘optional features’ line describes the available built-in databases. Notice that the ‘cache’ database, in contrast to the rest of databases, has two expiration periods associated with it. This is explained in the next subsection.
Mailfromd Manual:
The version 8.14 runs the following database types (or formats):
Cache database keeps the information about external emails, obtained using sender verification functions (see Checking Sender Address). The key entry to this database is an email address or email:sender-ip string, for addresses checked using strict verification. The data its stores for each key are:
success or
not_found, meaning the address is confirmed to exists or it
is not.
The ‘cache’ database has two expiration periods: a
positive expiration period, that is applied to entries with
the first field set to success, and a negative expiration
period, applied to entries marked as not_found.
The mail sending rate data, maintained by rate function
(see Rate limiting functions). A record consists of the following fields:
The time when the entry was entered into the database.
Interval during which the rate was measured (seconds).
Number of mails sent during this interval.
This database is maintained by tbf_rate function (see TBF).
Each record represents a single bucket and consists of the following
keys:
Timestamp of most recent token, as a 64-bit unsigned integer (microseconds resolution).
Estimated time when this bucket expires (seconds since epoch).
Number of tokens in the bucket (size_t).
This database is maintained by greylist function
(see Greylisting). Each record holds only the timestamp.
Its semantics depends on the greylisting implementation in
use (see greylisting types). In traditional implementation, it
is the time when the entry was entered into the database. In Con
Tassios implementation, it is the time when the greylisting period
expires.
Mailfromd Manual:
The mfdbtool utility is provided for performing various
operations on the mailfromd database.
To list the contents of a database, use --list option. When used without any arguments it will list the ‘cache’ database:
$ mfdbtool --list abrakat@mail.com success Thu Aug 24 15:28:58 2006 baccl@EDnet.NS.CA not_found Fri Aug 25 10:04:18 2006 bhzxhnyl@chello.pl not_found Fri Aug 25 10:11:57 2006 brqp@aaanet.ru:24.1.173.165 not_found Fri Aug 25 14:16:06 2006
You can also list data for any particular key or keys. To do so,
give the keys as arguments to mfdbtool:
$ mfdbtool --list abrakat@mail.com brqp@aaanet.ru:24.1.173.165 abrakat@mail.com success Thu Aug 24 15:28:58 2006 brqp@aaanet.ru:24.1.173.165 not_found Fri Aug 25 14:16:06 2006
To list another database, give its format identifier with the --format (-H) option. For example, to list the ‘rate’ database:
$ mfdbtool --list --format=rate sam@mail.net-62.12.4.3 Wed Sep 6 19:41:42 2006 139 3 0.0216 6.82e-06 axw@rame.com-59.39.165.172 Wed Sep 6 20:26:24 2006 0 1 N/A N/A
The --format option can be used with any database management option, described below.
Another useful operation you can do while listing ‘rate’ database is the prediction of estimated time of sending, i.e. the time when the user will be able to send mail if currently his mail sending rate has exceeded the limit. This is done using --predict option. The option takes an argument, specifying the mail sending rate limit, e.g. (the second line is split for readability):
$ mfdbtool --predict="180 per 1 minute" ed@fae.net-21.10.1.2 Wed Sep 13 03:53:40 2006 0 1 N/A N/A; free to send service@19.netlay.com-69.44.129.19 Wed Sep 13 15:46:07 2006 7 2 0.286 0.0224; in 46 sec. on Wed Sep 13 15:49:00 2006
Notice, that there is no need to use --list --format=rate along with this option, although doing so is not an error.
To delete an entry from the database, use --delete option, for example: mfdbtool --delete abrakat@mail.com. You can give any number of keys to delete in the command line.
Mailfromd Manual:
There are two principal operations of database management:
expiration and compaction. Expiration consists in removing
expired entries from the database. In fact, it is rarely needed,
since the expired entries are removed in the process of normal
mailfromd work. Nevertheless, a special option is provided
in case an explicit expiration is needed (for example, before dumping
the database to another format, to avoid transferring useless
information).
The command line option --expire instructs
mfdbtool to delete expired entries from the specified database. As
usual, the database is specified using --format option. If
it is not given explicitly, ‘cache’ is assumed.
While removing expired entries the space they occupied is marked as free, so it can be used by subsequent inserts. The database does not shrink after expiration is finished. To actually return the unused space to the file system you should compact your database.
This is done by running mfdbtool --compact (and, optionally,
specifying the database to operate upon with --format
option). Notice, that compacting a database needs roughly as
much disk space on the partition where the database resides as is
currently used by the database. Database compaction runs in three phases.
First, the database is scanned and all non-expired records are stored
in the memory. Secondly, a temporary database is created in the state
directory and all the cached entries are flushed into it. This
database is named after the PID of the running
mfdbtool process. Finally, the temporary database is
renamed to the source database.
Both --compact and --expire can be applied to all databases by combining them with --all. It is useful, for example, in crontab files. For example, I have the following monthly job in my crontab:
0 1 1 * * /usr/bin/mfdbtool --compact --all
Mailfromd Manual:
It is important to check your filter script before actually starting to use it. There are several ways to do so.
To test the syntax of your filter script, use the --lint
option. It will cause mailfromd to exit
immediately after attempting to compile the script file. If the
compilation succeeds, the program will exit with code 0. Otherwise,
it will exit with error code 78 (‘configuration error’). In the
latter case, mailfromd will also print a diagnostic message,
describing the error along with the exact location where the error was
diagnosed, for example:
mailfromd: /etc/mailfromd.mf:39: syntax error, unexpected reject
The error location is indicated by the name of the file and the
number of the line when the error occurred. By using the
--location-column option you instruct mailfromd to
also print the column number. E.g. with this option the above
error message may look like:
mailfromd: /etc/mailfromd.mf:39.12 syntax error, unexpected reject
Here, ‘39’ is the line and ‘12’ is the column number.
For complex scripts you may wish to obtain a listing of variables used in the script. This can be achieved using --xref command line option:
The output it produces consists of four columns:
Either number or string.
Measured in words.
A comma-separated list of locations where the variable was referenced. Each location is represented as file:line. If several locations pertain to the same file, the file name is listed only once.
Here is an example of the cross-reference output:
$ mailfromd --xref Cross-references: ----------------- cache_used number 5 /etc/mailfromd.mf:48 clamav_virus_name string 9 /etc/mailfromd.mf:240,240 db string 15 /etc/mailfromd.mf:135,194,215 dns_record_ttl number 16 /etc/mailfromd.mf:136,172,173 ehlo_domain string 11 gltime number 13 /etc/mailfromd.mf:37,219,220,222,223 greylist_seconds_left number 1 /etc/mailfromd.mf:220,226,227 last_poll_host string 2
If the script passes syntax check, the next step is often to test if
it works as you expect it to. This is done with --test
(-t) command line option. This option runs the
envfrom handler (or another one, see below) and prints the
result of its execution.
When running your script in test mode, you will need to supply the
values of Sendmail macros it needs. You do this by placing
the necessary assignments in the command line. For example, this is
how to supply initial values for f and client_addr
macros:
$ mailfromd --test f=gray@gnu.org client_addr=127.0.0.1
You may also need to alter initial values of some global variables
your script uses. To do so, use -v (--variable)
command line option. This option takes a single argument consisting
of the variable name and its initial value, separated by an equals
sign. For example, here is how to change the value of
ehlo_domain global variable:
$ mailfromd -v ehlo_domain=mydomain.org
The --test option is often useful in conjunction with options --debug, --trace and --transcript (see Logging and Debugging. The following example shows what the author got while debugging the filter script described in Filter Script Example:
$ mailfromd --test --debug=50 f=gray@gnu.org client_addr=127.0.0.1 MX 20 mx20.gnu.org MX 10 mx10.gnu.org MX 10 mx10.gnu.org MX 20 mx20.gnu.org getting cache info for gray@gnu.org found status: success (0), time: Thu Sep 14 14:54:41 2006 getting rate info for gray@gnu.org-127.0.0.1 found time: 1158245710, interval: 29, count: 5, rate: 0.172414 rate for gray@gnu.org-127.0.0.1 is 0.162162 updating gray@gnu.org-127.0.0.1 rates SET REPLY 450 4.7.0 Mail sending rate exceeded. Try again later State envfrom: tempfail
To test any handler, other than ‘envfrom’, give its name as the argument to --test option. Since this argument is optional, it is important that it be given immediately after the option, without any intervening white space, for example mailfromd --test=helo, or mailfromd -thelo.
This method allows to test one handler at a time. To test the
script as a whole, use mtasim utility. When
started it enters interactive mode, similar to that of
sendmail -bs, where it expects SMTP commands on
its standard input and sends answers to the standard output. The
--port=auto command line option instructs it to start
mailfromd and to create a unique socket for communication
with it. For the detailed description of the program and the ways to
use it, See mtasim.
Mailfromd Manual:
Mailfromd provides a special option that allows to run arbitrary MFL scripts. This is an experimental feature, intended for future use of MFL as a scripting language.
When given the --run command line option,
mailfromd loads the script given in its command line and
executes a function called ‘main’.
The function main must be declared as:
func main(...) returns number
Mailfromd passes all command line arguments that follow the script
name as arguments to that function. When the function returns, its
return value is used by mailfromd as exit code.
As an example, suppose the file script.mf contains the following:
func main (...)
returns number
do
loop for number i 1,
while i <= $#,
set i i + 1
do
echo "arg %i=" . $(i)
done
done
This function prints all its arguments (See variadic functions, for a detailed description of functions with variable number of arguments). Now running:
$ mailfromd --run script.mf 1 file dest
displays the following:
arg 1=1 arg 2=file arg 3=dest |
Note, that MFL does not have a direct equivalent of
shell’s $0 argument. If your function needs to know the name
of the script that is being executed, use __file__ built-in
constant instead (see __file__.
You may name your start function with any name other than the default
‘main’. In this case, give its name as an argument to the
--run option. This argument is optional, therefore it must
be separated from the option by an equals sign (with no whitespace
from either side). For example, given the command line below,
mailfromd loads the file script.mf and execute the
function named ‘start’:
$ mailfromd --run=start script.mf
Mailfromd Manual:
The --run option makes it possible to use mailfromd
scripts as standalone programs. The traditional way to do so was to
set the executable bit on the script file and to begin the script with
the interpreter selector, i.e. the characters ‘#!’ followed by
the name of the mailfromd executable, e.g.:
#! /usr/sbin/mailfromd --run
This would cause the shell to invoke mailfromd with the
command line constructed from the --run option, the name
of the invoked script file itself, and any actual arguments from
the invocation. Once invoked, mailfromd would treat the
initial ‘#!’ line as a usual single-line comment
(see Comments).
However, the interpretation of the ‘#!’ by shells has various
deficiencies, which depend on the actual shell being used. For
example, some shells pass any characters following the whitespace
after the interpreter name as a single argument, some others silently
truncate the command line after some number of characters, etc. This
often make it impossible to pass additional arguments to
mailfromd. For example, a script which begins with the
following line would most probably fail to be executed properly:
#! /usr/sbin/mailfromd --no-config --run
To compensate for these deficiencies and to allow for more complex
invocation sequences, mailfromd handles initial ‘#’
in a special way. If the first line of a source file begins with
‘#!/’ or ‘#! /’ (with a single space between ‘!’ and
‘/’), it is treated as a start of a multi-line comment, which is
closed by the two characters ‘!#’ on a line by themselves.
Thus, the correct way to begin a mailfromd script is:
#! /usr/sbin/mailfromd --run !#
Using this feature, you can start the mailfromd with
arbitrary shell code, provided it ends with an exec statement
invoking the interpreter itself. For example:
#!/bin/sh exec /usr/sbin/mailfromd --no-config --run $0 $@ !# func main(...) returns number do /* actual mfl code goes here */ done
Note the use of ‘$0’ and ‘$@’ to pass the actual script file
name and command line arguments to mailfromd.
Mailfromd Manual:
A special function is provided to break (parse) options in command lines, and to check for legal options. It uses the GNU getopt routines (see getopt in The GNU C Library Reference Manual).
The getopt function parses the command line arguments, as
supplied by argc and argv. The argc argument is the
argument count, and argv is an opaque data structure,
representing the array of arguments9. The operator vaptr (see vaptr) is
provided to initialize this argument.
An argument that starts with ‘-’ (and is not exactly ‘-’ or ‘--’), is an option element. An argument that starts with a ‘-’ is called short or traditional option. The characters of this element, except for the initial ‘-’ are option characters. Each option character represents a separate option. An argument that starts with ‘--’ is called long or GNU option. The characters of this element, except for the initial ‘--’ form the option name.
Options may have arguments. The argument to a short option is supplied immediately after the option character, or as the next word in command line. E.g., if option -f takes a mandatory argument, then it may be given either as -farg or as -f arg. The argument to a long option is either given immediately after it and separated from the option name by an equals sign (as --file=arg), or is given as the next word in the command line (e.g. --file arg).
If the option argument is optional, i.e. it may not necessarily be given, then only the first form is allowed (i.e. either -farg or --file=arg.
The ‘--’ command line argument ends the option list. Any arguments following it are not considered options, even if they begin with a dash.
If getopt is called repeatedly, it returns successively each of
the option characters from each of the option elements (for short
options) and each option name (for long options). In this case, the
actual arguments are supplied only to the first invocation.
Subsequent calls must be given two nulls as arguments. Such
invocation instructs getopt to use the values saved on the
previous invocation.
When the function finds another option, it returns its character or name
updating the external variable optind (see below) so that the
next call to getopt can resume the scan with the following
option.
When there are no more options left, or a ‘--’ argument is
encountered, getopt returns an empty string. Then
optind gives the index in argv of the first element that
is not an option.
The legitimate options and their characteristics are supplied in
additional arguments to getopt. Each such argument is a string
consisting of two parts, separated by a vertical bar (‘|’). Any
one of these parts is optional, but at least one of them must be
present. The first part specifies short option character. If it is
followed by a colon, this character takes mandatory argument. If it
is followed by two colons, this character takes an optional argument.
If only the first part is present, the ‘|’ separator may be
omitted. Examples:
Short option -c.
Short option -f, taking a mandatory argument.
Short option -f, taking an optional argument.
If the vertical bar is present and is followed by any characters, these characters specify the name of a long option, synonymous to the short one, specified by the first part. Any mandatory or optional arguments to the short option remain mandatory or optional for the corresponding long option. Examples:
Short option -f, or long option --file, requiring an argument.
Short option -f, or long option --file, taking an optional argument.
In any of the above cases, if this option appears in the command line,
getopt returns its short option character.
To define a long option without a short equivalent, begin it with a bar, e.g.:
If this option is to take an argument, this is specified using the mechanism described above, except that the short option character is replaced with a minus sign. For example:
Long option --output, which takes a mandatory argument.
Long option --output, which takes an optional argument.
If an option is returned that has an argument in the command line,
getopt stores this argument in the variable optarg.
After each invocation, getopt sets the variable optind
to the index of the next argv element to be parsed. Thus,
when the list of options is exhausted and the function returned an
empty string, optind contains the index of the the first
element that is not an option.
When getopt encounters an option that is not described in its
arguments or if it detects a missing option argument it prints an
error message using mailfromd logging facilities, stores
the offending option in the variable optopt, and returns ‘?’.
If printing error message is not desired (e.g. the application is going
to take care of error messaging), it can be disabled by setting the
variable opterr to ‘0’.
The third argument to getopt, called controlling argument,
may be used to control the behavior of the function. If it is a
colon, it disables printing the error message for unrecognized options
and missing option arguments (as setting opterr to ‘0’
does). In this case getopt returns ‘:’, instead of
‘?’ to indicate missing option argument.
If the controlling argument is a plus sign, or the environment
variable POSIXLY_CORRECT is set, then option processing stops as
soon as a non-option argument is encountered. By default, if options
and non optional arguments are intermixed in argv, getopt
permutes them so that the options go first, followed by non-optional
arguments.
If the controlling argument is ‘-’, then each non-option element in argv is handled as if it were the argument of an option with character code 1 (‘"\001"’, in MFL notation. This can used by programs that are written to expect options and other argv-elements in any order and that care about the ordering of the two.
Any other value of the controlling argument is handled as an option definition.
A special language construct is provided to supply the second
argument (argv) to getopt and similar functions:
vaptr(param)
where param is a positional parameter, from which to start the array of argv. For example:
func main(...) returns number do set rc getopt($#, vaptr($1), "|help") ...
Here, vaptr($1) constructs the argv array from all the
arguments, supplied to the function main.
To illustrate the use of getopt function, let’s suppose you
write a script that takes the following options:
Then, the corresponding getopt invocation will be:
func main(...)
returns number
do
loop for string rc getopt($#, vaptr($1),
"f:|file", "-::|output", "h|help"),
while rc != "",
set rc getopt(0, 0)
do
switch rc
do
case "f":
set file optarg
case "output"
set output 1
set output_dir optarg
case "h"
help()
default:
return 1
done
...
Mailfromd Manual:
Depending on its operation mode, mailfromd tries to guess
whether it is appropriate to print its diagnostics and informational
messages on standard error or to send them to syslog. Standard error
is assumed if the program is run with one of the following command
line options:
If none of these are used, mailfromd switches to syslog as
soon as it finishes its startup. There are two ways to communicate
with the syslogd daemon: using the syslog
function from the system libc library, which is a blocking
implementation in most cases, or via internal, asynchronous,
syslog implementation. Whether the latter is compiled in and which
implementation is used by default is determined when compiling
the package, as described in Using non-blocking syslog.
The --logger command line option allows you to manually select the diagnostic channel:
Log everything to the standard error.
Log to syslog.
Log to syslog using the asynchronous syslog implementation.
Another way to select the diagnostic channel is by using the
logger statement in the configuration file. The statement
takes the same argument as its command line counterpart.
The rest of details regarding diagnostic output are controlled by
the logging configuration statement.
The default syslog facility is ‘mail’; it can be changed
using the --log-facility command line option or
facility statement. Argument in both cases is a valid
facility name, i.e. one of: ‘user’, ‘daemon’,
‘auth’, ‘authpriv’, ‘mail’, and ‘local0’
through ‘local7’. The argument can be given in upper, lower or
mixed cases, and it can be prefixed with ‘log_’:
Another syslog-related parameter that can be configured is the
tag, which identifies mailfromd messages. The default tag
is the program name. It is changed by the --log-tag
(-L command line option and the tag logging statement.
The following example configures both the syslog facility and tag:
logging {
facility local7;
tag "mfd";
}
As any other UNIX utility, mailfromd is very quiet unless it
has something important to communicate, such as, e.g. an error condition.
A set of command line options is provided for
controlling the verbosity of its output.
The --trace option enables tracing Sendmail actions
executed during message verifications. When this option is given,
any accept, discard, continue, etc. triggered
during execution of your filter program will leave their traces in
the log file. Here is an example of how it looks like (syslog time
stamp, tag and PID removed for readability):
k8DHxvO9030656: /etc/mailfromd.mf:45: reject 550 5.1.1 Sender validity not confirmed
This shows that while verifying the message with ID
‘k8DHxvO9030656’ the reject action was executed by filter
script /etc/mailfromd.mf at line 45.
The use of message ID in the log deserves a special
notice. The program will always identify its log messages with
the ‘Message-Id’, when it is available. Your responsibility as an
administrator is to make sure it is available by configuring
your MTA to export the macro ‘i’ to mailfromd.
The rule of thumb is: make ‘i’ available to the very first
handler mailfromd executes. It is not necessary to export
it to the rest of the handlers, since mailfromd will cache
it. For example, if your filter script contains ‘envfrom’ and
‘envrcpt’ handlers, export ‘i’ for ‘envfrom’.
The exact instructions on how to ensure it depend on the
MTA you use. For ‘Sendmail’, refer to Sendmail.
For MeTA1, see MeTA1, and pmult-macros. For
‘Postfix’, see Postfix.
To push log verbosity further, use the debug
configuration statement (see conf-debug) or its command line
equivalent, --debug (-d, see --debug). Its
argument is a debugging level, whose syntax is described
in http://mailutils.org/wiki/Debug_level.
The debugging output is controlled by a set of levels, each of which can be set independently of others. Each debug level consists of a category name, which identifies the part of package for which additional debugging is desired, and a level number, which indicates how verbose should its output be.
Valid debug levels are:
Displays error conditions which are normally not reported, but passed to the caller layers for handling.
Ten levels of verbosity, trace0 producing less output,
trace9 producing the maximum amount of output.
Displays network protocol interaction, where applicable.
The overall debugging level is specified as a list of individual levels, delimited with semicolons. Each individual level can be specified as one of:
Disables all levels for the specified category.
Enables all levels for the specified category.
For this category, enables all levels from ‘error’ to level, inclusive.
Enables only the given level in this category.
Disables all levels from ‘error’ to level, inclusive, in this category.
Disables only the given level in this category.
Enables all levels in the range from levelA to levelB, inclusive.
Disables all levels in the range from levelA to levelB, inclusive.
Additionally, a comma-separated list of level specifications is allowed after the dot. For example, the following specification:
acl.prot,!=trace9,!trace2
enables in category acl all levels, except trace9, trace0, trace1, and trace2.
Implementation and applicability of each level of debugging differs between various categories. Categories built-in to mailutils are described in http://mailutils.org/wiki/Debug_level. Mailfromd introduces the following additional categories:
Detailed debugging info about expiration and compaction.
List records being removed.
Verbose information about attempted DNS queries and their results.
Enables ‘libadns’ internal debugging.
Additional information about normal conditions, such as subprocess exiting successfully or a remote party being allowed access by ACL.
Detailed transcript of server manager actions: startup, shutdown, subprocess cleanups, etc.
Additional info about fd sets.
Individual subserver status information.
Subprocess registration.
Verbosely list incoming connections, functions being executed and erroneous conditions: missing headers in SMFIR_CHGHEADER, undefined macros, etc.
List milter requests being processed.
List SMTP body content in SMFIR_REPLBODY requests.
Verbosely list mild errors encountered: bad recipient addresses, etc.
Verification session transcript.
MX servers checks.
List emails being checked.
Additional info.
Info about hostnames in relayed domain list
Debugging of the virtual engine.
Message modification lists.
Debug message modification operations and Sendmail macros registered.
List SMTP stages (‘xxfi_*’ calls).
Cleanup calls.
Preprocessor.
Show command line of the preprocessor being run.
Stack operations
Debug exception state save/restore operations.
Mild errors.
List calls to ‘spf_eval_record’, ‘spf_test_record’, ‘spf_check_host_internal’, etc.
General debug info.
Explicitly list A records obtained when processing the ‘a’ SPF mechanism.
Categories starting with ‘bi_’ debug built-in modules:
Database functions.
List database look-ups.
Trace operations on the greylisting database.
SpamAssassin and ClamAV API.
Report the findings of the ‘clamav’ function.
Trace payload in interactions with ‘spamd’.
I/O functions.
Debug the following functions: open, spawn, write.
Report stderr redirection.
Report external commands being run.
Mailbox functions.
Report opened mailboxes.
Other built-ins.
Report results of checks for existence of usernames.
For example, the following invocation enables levels up to ‘trace2’ in category ‘engine’, all levels in category ‘savsrv’ and levels up to ‘trace0’ in category ‘srvman’:
$ mailfromd --debug='engine.trace2;savsrv;srvman.trace0'
You need to have sufficient knowledge about mailfromd
internal structure to use this form of the --debug option.
To control the execution of the sender verification functions (see SMTP Callout functions), you may use --transcript (-X) command line option which enables transcripts of SMTP sessions in the logs. Here is an example of the output produced running mailfromd --transcript:
k8DHxlCa001774: RECV: 220 spf-jail1.us4.outblaze.com ESMTP Postfix k8DHxlCa001774: SEND: HELO mail.gnu.org.ua k8DHxlCa001774: RECV: 250 spf-jail1.us4.outblaze.com k8DHxlCa001774: SEND: MAIL FROM: <> k8DHxlCa001774: RECV: 250 Ok k8DHxlCa001774: SEND: RCPT TO: <t1Kmx17Q@malaysia.net> k8DHxlCa001774: RECV: 550 <>: No thank you rejected: Account Unavailable: Possible Forgery k8DHxlCa001774: poll exited with status: not_found; sent "RCPT TO: <t1Kmx17Q@malaysia.net>", got "550 <>: No thank you rejected: Account Unavailable: Possible Forgery" k8DHxlCa001774: SEND: QUIT
Mailfromd Manual:
A runtime error is a special condition encountered during
execution of the filter program, that makes further execution of
the program impossible. There are two kinds of runtime errors: fatal
errors, and uncaught exceptions. Whenever a runtime error occurs,
mailfromd writes into the log file the following message:
RUNTIME ERROR near file:line: text
where file:line indicates approximate source file location where the error occurred and text gives the textual description of the error.
Fatal runtime errors are caused by a condition that is impossible to fix at run time. For version 8.14 these are:
There is not enough memory for the execution of the program. Try to
make more memory available for mailfromd or to reduce
its memory requirements by rewriting your filter script.
These errors are reported when there is not enough space left on
stack to perform the requested operation, and the attempt to resize the stack
has failed. Usually mailfromd expands the stack when the need
arises (see automatic stack resizing). This runtime error
indicates that there were no more memory available for stack
expansion. Try to make more memory available for mailfromd
or to reduce its memory requirements by rewriting your filter script.
Program attempted to pop a value off the stack but the stack was
already empty. This indicates an internal error in the
MFL compiler or mailfromd runtime engine. If you
ever encounter this error,
please report it to bug-mailfromd@gnu.org.ua. Include
the log fragment (about 10-15 lines before and after this log message)
and your filter script. See Reporting Bugs, for more
information about bug reporting.
The program counter is out of allowed range. This is a severe
error, indicating an internal inconsistency in mailfromd
runtime engine. If you encounter it, please report it to
bug-mailfromd@gnu.org.ua. Include the log fragment (about
10-15 lines before and after this log message) and your filter script.
See Reporting Bugs, for more information about how to report a
bug.
These indicate a programmatic error in your filter script, which the MFL compiler was unable to discover at compilation stage:
The throw statement used a not existent exception number n.
Fix the statement and restart mailfromd. See throw, for
the information about throw statement and see Exceptions,
for the list of available exception codes.
You have used a back-reference (see Back references), where there is no previous regular expression to refer to. Fix this line in your code and restart the program.
You have used a back-reference (see Back references), with a number greater than the number of available groups in the previous regular expression. For example:
if $f matches "(.*)@gnu.org"
# Wrong: there is only one group in the regexp above!
set x \2
…
Fix your code and restart the daemon.
Another kind of runtime errors are uncaught exceptions, i.e. exceptional conditions for which no handler was installed (See Exceptions, for information on exceptions and on how to handle them). These errors mean that the programmer (i.e. you), made no provision for some specific condition. For example, consider the following code:
prog envfrom
do
if $f mx matches "yahoo.com"
foo()
fi
done
It is syntactically correct, but it overlooks the fact that mx
matches may generate e_temp_failure exception, if the underlying
DNS query has timed out (see Special comparisons). If
this happens, mailfromd has no instructions on what to do
next and reports an error. This can easily be fixed using a catch
statement, e.g.:
prog envfrom
do
# Catch DNS errors
catch e_temp_failure or e_failure
do
tempfail 451 4.1.1 "MX verification failed"
done
if $f mx matches "yahoo.com"
foo()
fi
done
Another common case are undefined Sendmail macros. In this case the
e_macroundef exception is generated:
RUNTIME ERROR near foo.c:34: Macro not defined: {client_adr}
These can be caused either by misspelling the macro name (as in the example message above) or by failing to export the required name in Sendmail milter configuration (see exporting macros). This error should be fixed either in your source code or in sendmail.cf file, but if you wish to provide a special handling for it, you can use the following catch statement:
catch e_macroundef do … done
Sometimes the location indicated with the runtime error message is
not enough to trace the origin of the error. For example, an error
can be generated explicitly with throw statement
(see throw):
RUNTIME ERROR near match_cidr.mf:30: invalid CIDR (text)
If you look in module match_cidr.mf, you will see the following code (line numbers added for reference):
23 func match_cidr(string ipstr, string cidr) returns number
24 do
25 number netmask
26
27 if cidr matches '^(([0-9]{1,3}\.){3}[0-9]{1,3})/([0-9][0-9]?)'
28 return inet_aton(ipstr) & len_to_netmask(\3) = inet_aton(\1)
29 else
30 throw invcidr "invalid CIDR (%cidr)"
31 fi
32 return 0
33 done
Now, it is obvious that the value of cidr argument to
match_cidr was wrong, but how to find the caller that passed
the wrong value to it? The special command line option
--stack-trace is provided for this. This option enables
dumping stack traces when a fatal error occurs. The traces
contain information about function calls. Continuing our example,
using the --stack-trace option you will see the following diagnostics:
RUNTIME ERROR near match_cidr.mf:30: invalid CIDR (127%) mailfromd: Stack trace: mailfromd: 0077: match_cidr.mf:30: match_cidr mailfromd: 0096: test.mf:13: bar mailfromd: 0110: mailfromd.mf:18: foo mailfromd: Stack trace finishes mailfromd: Execution of the configuration program was not finished
Each trace line describes one stack frame. The lines appear in the order of most recently called to least recently called. Each frame consists of:
Thus, the example above can be read as: “the function
match_cidr was called by the function bar in file
test.mf at line 13. This function was called from
the function bar, in file test.mf at line 13. In its turn,
bar was called by the function foo, in file
mailfromd.mf at line 18”.
Examining caller functions will help you localize the source of the error and fix it.
You can also request a stack trace any place in your code, by
calling the stack_trace function. This can be useful for
debugging, or in your catch statements.
Mailfromd Manual:
This section discusses some potential culprits in the MFL.
It is important to execute special caution when writing format
strings for sprintf (see String formatting) and strftime
(see strftime) functions. They use ‘%’ as a character
introducing conversion specifiers, while the same character is used to
expand a MFL variable within a string. To prevent this
misinterpretation, always enclose format specification in single
quotes (see singe-vs-double). To illustrate this, let’s consider
the following example:
echo sprintf ("Mail from %s", $f)
If a variable s is not declared, this line will produce the
‘Variable s is not defined’ error message, which will allow you
to identify and fix the bug. The situation is considerably worse if
s is declared. In that case you will see no warning message,
as the statement is perfectly valid, but at the run-time the variable
s will be interpreted within the format string, and its value
will replace %s. To prevent this from happening, single quotes
must be used:
echo sprintf ('Mail from %s', $f)
This does not limit the functionality, since there is no need to fall back to variable interpretation in format strings.
Yet another dangerous feature of the language is the way to refer to variable and constant names within literal strings. To expand a variable or a constant the same notation is used (See Variables, and see Constants). Now, lets consider the following code:
const x 2 string x "X" prog envfrom do echo "X is %x" done
Does %x in echo refers to the variable or to the
constant? The correct answer is ‘to the variable’. When executed, this
code will print ‘X is X’.
As of version 8.14, mailfromd will always print a
diagnostic message whenever it stumbles upon a variable having the
same name as a previously defined constant or vice versa. The
resolution of such name clashes is described in detail in
See variable--constant shadowing.
Future versions of the program may provide a non-ambiguous way of referring to variables and constants from literal strings.
Mailfromd Manual:
The mail filtering language, or MFL, is a special language designed for writing filter scripts. It has a simple syntax, similar to that of Bourne shell. In contrast to the most existing programming languages, MFL does not have any special terminating or separating characters (like, e.g. newlines and semicolons in shell)10. All syntactical entities are separated by any amount of white-space characters (i.e. spaces, tabulations or newlines).
The following sections describe MFL syntax in detail.
Mailfromd Manual:
Two types of comments are allowed: C-style, enclosed between ‘/*’ and ‘*/’, and shell-style, starting with ‘#’ character and extending up to the end of line:
/* This is a comment. */ # And this too.
There are, however, several special cases, where the characters following ‘#’ are not ignored.
If the first line begins with ‘#!/’ or ‘#! /’, this is treated as a start of a multi-line comment, which is closed by the characters ‘!#’ on a line by themselves. This feature allows for writing sophisticated scripts. See top-block, for a detailed description.
If ‘#’ is followed by word ‘include’ (with optional whitespace between them), this statement requires inclusion of the specified file, as in C. There are two forms of the ‘#include’ statement:
#include <file>
#include "file"
The quotes around file in the second form quotes are optional.
Both forms are equivalent if file is an absolute file name. Otherwise, the first form will look for file in the include search path. The second one will look for it in the current working directory first, and, if not found there, in the include search path.
The default include search path is:
Where prefix is the installation prefix.
New directories can be appended in front of it using -I
(--include) command line option, or include-path
configuration statement (see include-path).
For example, invoking
$ mailfromd -I/var/mailfromd -I/com/mailfromd
creates the following include search path
Along with #include, there is also a special form
#include_once, that has the same syntax:
#include_once <file> #include_once "file"
This form works exactly as #include, except that, if the
file has already been included, it will not be included
again. As the name suggests, it will be included only once.
This form should be used to prevent re-inclusions of a code, which can cause problems due to function redefinitions, variable reassignments etc.
A line in the form
#line number "identifier"
causes the MFL compiler to believe, for purposes of error diagnostics, that the line number of the next source line is given by number and the current input file is named by identifier. If the identifier is absent, the remembered file name does not change.
Mailfromd Manual:
If ‘#’ is immediately followed by word ‘pragma’ (with optional whitespace between them), such a construct introduces a pragmatic comment, i.e. an instruction that controls some configuration setting.
The available pragma types are described in the following subsections.
Mailfromd Manual:
The #pragma prereq statement ensures that the correct
mailfromd version is used to compile the source file it
appears in. It takes version number as its arguments and produces
a compilation error if the actual mailfromd version number
is earlier than that. For example, the following statement:
#pragma prereq 7.0.94
results in error if compiled with mailfromd version 7.0.93
or prior.
Mailfromd Manual:
The stacksize pragma sets the initial size of the run-time
stack and may also define the policy of its growing, in case it
becomes full. The default stack size is 4096 words. You may
need to increase this number if your configuration program uses
recursive functions or does an excessive amount of string manipulations.
Sets stack size to size units. Optional incr and max define stack growth policy (see below). The default units are words. The following example sets the stack size to 7168 words:
#pragma stacksize 7168
The size may end with a unit size suffix:
| Suffix | Meaning |
|---|---|
| k | Kiloword, i.e. 1024 words |
| m | Megawords, i.e. 1048576 words |
| g | Gigawords, |
| t | Terawords (ouch!) |
Table 4.1: Unit Size Suffix
File suffixes are case-insensitive, so the following two pragmas are
equivalent and set the stack size to 7*1048576 = 7340032 words:
#pragma stacksize 7m #pragma stacksize 7M
When the MFL engine notices that there is no more stack space available, it attempts to expand the stack. If this attempt succeeds, the operation continues. Otherwise, a runtime error is reported and the execution of the filter stops.
The optional incr argument to #pragma stacksize defines growth
policy for the stack. Two growth policies are implemented:
fixed increment policy, which expands stack in a fixed
number of expansion chunks, and exponential growth policy, which
duplicates the stack size until it is able to accommodate the needed
number of words. The fixed increment policy is the default. The default
chunk size is 4096 words.
If incr is the word ‘twice’, the duplicate policy is selected. Otherwise incr must be a positive number optionally suffixed with a size suffix (see above). This indicates the expansion chunk size for the fixed increment policy.
The following example sets initial stack size to 10240, and expansion chunk size to 2048 words:
#pragma stacksize 10M 2K
The pragma below enables exponential stack growth policy:
#pragma stacksize 10240 twice
In this case, when the run-time evaluator hits the stack size limit, it expands the stack to twice the size it had before. So, in the example above, the stack will be sequentially expanded to the following sizes: 20480, 40960, 81920, 163840, etc.
The optional max argument defines the maximum size of the stack. If stack grows beyond this limit, the execution of the script will be aborted.
If you are concerned about the execution time of your script, you
may wish to avoid stack reallocations. To help you find out the
optimal stack size, each time the stack is expanded,
mailfromd issues a warning in its log file, which looks like
this:
warning: stack segment expanded, new size=8192
You can use these messages to adjust your stack size configuration settings.
Mailfromd Manual:
The ‘#pragma regex’, controls compilation of regular expressions. You can use any number of such pragma directives in your mailfromd.mf. The scope of ‘#pragma regex’ extends to the next occurrence of this directive or to the end of the script file, whichever occurs first.
The optional push|pop parameter is one of the words ‘push’ or ‘pop’ and is discussed in detail below. The flags parameter is a whitespace-separated list of regex flags. Each regex-flag is a word specifying some regex feature. It can be preceded by ‘+’ to enable this feature (this is the default), by ‘-’ to disable it or by ‘=’ to reset regex flags to its value. Valid regex-flags are:
Use POSIX Extended Regular Expression syntax when interpreting regex. If not set, POSIX Basic Regular Expression syntax is used.
Do not differentiate case. Subsequent regex searches will be case insensitive.
Match-any-character operators don’t match a newline.
A non-matching list (‘[^...]’) not containing a newline does not match a newline.
Match-beginning-of-line operator (‘^’) matches the empty string immediately after a newline.
Match-end-of-line operator (‘$’) matches the empty string immediately before a newline.
For example, the following pragma enables POSIX extended, case insensitive matching (a good thing to start your mailfromd.mf with):
#pragma regex +extended +icase
Optional modifiers ‘push’ and ‘pop’ can be used to maintain a stack of regex flags. The statement
#pragma regex push [flags]
saves current regex flags on stack and then optionally modifies them as requested by flags.
The statement
#pragma regex pop [flags]
does the opposite: restores the current regex flags from the top of stack and applies flags to it.
This statement is useful in module and include files to avoid disturbing user regex settings. E.g.:
#pragma regex push +extended +icase . . . #pragma regex pop
Mailfromd Manual:
This pragma configures properties for a DBM database. See Database functions, for its detailed description.
Mailfromd Manual:
Selects the greylisting implementation to use. Allowed values for type are:
Use the traditional greylisting implementation. This is the default.
Use Con Tassios greylisting implementation.
See greylisting types, for a detailed description of these greylisting implementations.
Notice, that this pragma can be used only once. A second use of this pragma would constitute an error, because you cannot use both greylisting implementations in the same program.
Mailfromd Manual:
Declare that the Milter stage handler uses MTA macro listed as the rest of arguments. The handler must be a valid handler name (see Handlers).
The mailfromd parser collects the names of the macros
referred to by a ‘$name’ construct within a handler
(see Sendmail Macros) and declares them automatically for
corresponding handlers. It is, however, unable to track macros
used in functions called from handler as well as those referred to
via getmacro and macro_defined functions. Such
macros should be declared using ‘#pragma miltermacros’.
During initial negotiation with the MTA,
mailfromd will ask it to export the macro names declared
automatically or by using the ‘#pragma miltermacros’. The
MTA is free to honor or to ignore this request. In
particular, Sendmail versions prior to 8.14.0 and Postfix versions
prior to 2.5 do not support this feature. If you use one of these,
you will need to export the needed macros explicitly in the
MTA configuration. For more details, refer to the section
in MTA Configuration corresponding to your MTA type.
Mailfromd Manual:
The #pragma provide-callout statement is used in the
callout module to inform mailfromd that the
module has been loaded.
Do not use this pragma.
Mailfromd Manual:
The mailfromd filter script language operates on entities
of two types: numeric and string.
The numeric type is represented internally as a signed long integer. Depending on the machine architecture, its size can vary. For example, on machines with Intel-based CPUs it is 32 bits long.
A string is a string of characters of arbitrary length. Strings can contain any characters except ASCII NUL.
There is also a generic pointer, which is designed to
facilitate certain operations. It appears only in body
handler. See body handler, for more information about it.
Mailfromd Manual:
A decimal number is any sequence of decimal digits, not beginning with ‘0’.
An octal number is ‘0’ followed by any number of octal
digits (‘0’ through ‘7’), for example: 0340.
A hex number is ‘0x’ or ‘0X’ followed by any number
of hex digits (‘0’ through ‘9’ and ‘a’ through ‘f’
or ‘A’ through ‘F’), for example: 0x3ef1.
Mailfromd Manual:
A literal is any sequence of characters enclosed in single or double quotes.
After tempfail and reject actions two special kinds of
literals are recognized: three-digit numeric values represent
RFC 2821 reply codes, and literals consisting of tree digit
groups separated by dots represent an extended reply code as per
RFC 1893/2034. For example:
510 # A reply code 5.7.1 # An extended reply code
String literals enclosed in double quotation marks (double-quoted strings) are subject to backslash interpretation, macro expansion, variable interpretation and back reference interpretation.
Backslash interpretation is performed at compilation time. It consists in replacing the following escape sequences with the corresponding single characters:
| Sequence | Replaced with |
| \a | Audible bell character (ASCII 7) |
| \b | Backspace character (ASCII 8) |
| \f | Form-feed character (ASCII 12) |
| \n | Newline character (ASCII 10) |
| \r | Carriage return character (ASCII 13) |
| \t | Horizontal tabulation character (ASCII 9) |
| \v | Vertical tabulation character (ASCII 11) |
Table 4.2: Backslash escapes
In addition, the sequence ‘\newline’ has the same effect as ‘\n’, for example:
"a string with\ embedded newline" "a string with\n embedded newline"
Any escape sequence of the form ‘\xhh’, where h denotes any hex digit is replaced with the character whose ASCII value is hh. For example:
"\x61nother" ⇒ "another"
Similarly, an escape sequence of the form ‘\0ooo’, where o is an octal digit, is replaced with the character whose ASCII value is ooo.
Macro expansion and variable interpretation occur at run-time. During
these phases all Sendmail macros (see Sendmail Macros),
mailfromd variables (see Variables), and constants
(see Constants) referenced in the string are replaced by their
actual values. For example, if the Sendmail macro f has the
value ‘postmaster@gnu.org.ua’ and the variable last_ip
has the value ‘127.0.0.1’, then the
string11
"$f last connected from %last_ip;"
will be expanded to
"postmaster@gnu.org.ua last connected from 127.0.0.1;"
A back reference is a sequence ‘\d’, where d
is a decimal number. It refers to the dth parenthesized
subexpression in the last matches statement12. Any back reference occurring within a
double-quoted string is replaced by the value of the corresponding
subexpression. See Special comparisons, for a detailed
description of this process. Back reference interpretation is
performed at run time.
Any characters enclosed in single quotation marks are read unmodified.
The following examples contain pairs of equivalent strings:
"a string" 'a string' "\\(.*\\):" '\(.*\):'
Notice the last example. Single quotes are particularly useful in writing regular expressions (see Special comparisons).
Mailfromd Manual:
Here-document is a special form of a string literal is, allowing to specify multiline strings without having to use backslash escapes. The format of here-documents is:
<<[flags]word … word
The <<word construct instructs the parser to read all
the following lines up to the line containing only word, with
possible trailing blanks. The lines thus read are concatenated
together into a single string. For example:
set str <<EOT A multiline string EOT
The body of a here-document is interpreted the same way as
double-quoted strings (see Double-quoted strings). For example,
if Sendmail macro f has the value jsmith@some.com and
the variable count is set to 10, then the following string:
set s <<EOT <$f> has tried to send %count mails. Please see docs for more info. EOT
will be expanded to:
<jsmith@some.com> has tried to send 10 mails. Please see docs for more info.
If the word is quoted, either by enclosing it in single quote characters or by prepending it with a backslash, all interpretations and expansions within the document body are suppressed. For example:
set s <<'EOT' The following line is read verbatim: <$f> has tried to send %count mails. Please see docs for more info. EOT
Optional flags in the here-document construct control the way
leading white space is handled. If flags is - (a dash),
then all leading tab characters are stripped from input lines and the
line containing word. Furthermore, if - is followed by a
single space, all leading whitespace is stripped from them. This
allows here-documents within configuration scripts to be indented in a
natural fashion. Examples:
<<- TEXT
<$f> has tried to send %count mails.
Please see docs for more info.
TEXT
Here-documents are particularly useful with reject actions
(see reject.
Mailfromd Manual:
Sendmail macros are referenced exactly the same way they are in
sendmail.cf configuration file, i.e. ‘$name’,
where name represents the macro name. Notice, that the notation
is the same for both single-character and multi-character macro names.
For consistency with the Sendmail configuration the
‘${name}’ notation is also accepted.
Another way to reference Sendmail macros is by using function
getmacro (see Macro access).
Sendmail macros evaluate to string values.
Notice, that to reference a macro, you must properly export it in
your MTA configuration. Attempt to reference a not exported
macro will result in raising a e_macroundef exception at the run time
(see uncaught exceptions).
Mailfromd Manual:
A constant is a symbolic name for an MFL value.
Constants are defined using const statement:
[qualifier] const name expr
where name is an identifier, and expr is any valid
MFL expression evaluating immediately to a constant literal
or numeric value. Optional qualifier defines the scope of
visibility for that constant (see scope of visibility): either
public or static.
Once defined, any appearance of name in the program text is replaced by its value. For example:
const x 10/5 const text "X is "
defines the numeric constant ‘x’ with the value ‘5’, and the literal constant ‘text’ with the value ‘X is ’.
A special construct is provided to define a series of numeric constants (an enumeration):
[qualifier] const do name0 [expr0] name1 [expr1] ... nameN [exprN] done
Each exprN, if present, must evaluate to a constant numeric expression. The resulting value will be assigned to constant nameN. If exprN is not supplied, the constant will be defined to the value of the previous constant plus one. If expr0 is not supplied, 0 is assumed.
For example, consider the following statement
const do A B C 10 D done
This defines ‘A’ to 0, ‘B’ to 1, ‘C’ to 10 and ‘D’ to 11.
As a matter of fact, exprN may also evaluate to a constant string expression, provided that all expressions in the enumeration ‘const’ statement are provided. That is, the following is correct:
const do A "one" B "two" C "three" D "four" done
whereas the following is not:
const do A "one" B C "three" D "four" done
Trying to compile the latter example will produce:
mailfromd: filename:5.3: initializer element is not numeric
which means that mailfromd was trying to create constant
‘B’ with the value of ‘A’ incremented by one, but was unable
to do so, because the value in question was not numeric.
Constants can be used in normal MFL expressions as well as in literals. To expand a constant within a literal string, prepend a percent sign to its name, e.g.:
echo "New %text %x" ⇒ "New X is 2"
This way of expanding constants creates an ambiguity if there happen to be a variable of the same name as the constant. See variable--constant clashes, for more information of this case and ways to handle it.
Mailfromd Manual:
Several constants are built into the MFL compiler. To discern them from user-defined ones, their names start and end with two underscores (‘__’).
The following constants are defined in mailfromd version
8.14:
Expands to the name of the current source file.
Expands to the name of the current lexical context, i.e. the function or handler name.
This built-in constant is defined for alpha versions only. Its value is the Git tag of the recent commit corresponding to that version of the package. If the release contains some uncommitted changes, the value of the ‘__git__’ constant ends with the suffix ‘-dirty’.
Expands to the current line number in the input source file.
Expands to the major version number.
The following example uses __major__ constant to determine
if some version-dependent feature can be used:
if __major__ > 2
# Use some version-specific feature
fi
Expands to the minor version number.
Expands to the name of the current module (see Modules).
Expands to the package name (‘mailfromd’)
For alpha versions and maintenance releases expands to the version patch level. For stable versions, expands to ‘0’.
Expands to the default external preprocessor command line, if the preprocessor is used, or to an empty string if it is not, e.g.:
__defpreproc__ ⇒ "/usr/bin/m4 -s"
See Preprocessor, for information on preprocessor and its features.
Expands to the current external preprocessor command line, if the
preprocessor is used, or to an empty string if it is not. Notice,
that it equals __defpreproc__, unless the preprocessor was
redefined using --preprocessor command line option
(see –preprocessor).
Expands to the textual representation of the program version (e.g. ‘3.0.90’)
Expands to the default state directory (see statedir).
Expands to the current value of the program state directory
(see statedir). Notice, that it is the same as
__defstatedir__ unless the state directory was redefined at run
time.
Built-in constants can be used as variables, this allows to expand them within strings or here-documents. The following example illustrates the common practice used for debugging configuration scripts:
func foo(number x) do echo "%__file__:%__line__: foo called with arg %x" … done
If the function foo were called in line 28 of the
script file /etc/mailfromd.mf, like this:
foo(10), you will see the following string in your logs:
/etc/mailfromd.mf:28: foo called with arg 10
Mailfromd Manual:
Variables represent regions of memory used to hold variable data. These memory regions are identified by variable names. A variable name must begin with a letter or underscore and must consist of letters, digits and underscores.
Each variable is associated with its scope of visibility, which defines the part of source code where it can be used (see scope of visibility). Depending on the scope, we discern three main classes of variables: public, static and automatic (or local).
Public variables have indefinite lexical scope, so they may be referred to anywhere in the program. Static are variables visible only within their module (see Modules). Automatic or local variables are visible only within the given function or handler.
Public and static variables are sometimes collectively called global.
These variable classes occupy separate namespaces, so that an automatic variable can have the same name as an existing public or static one. In this case this variable is said to shadow its global counterpart. All references to such a name will refer to the automatic variable until the end of its scope is reached, where the global one becomes visible again.
Likewise, a static variable may have the same name as a static variable defined in another module. However, it may not have the same name as a public variable.
A variable is declared using the following syntax:
[qualifiers] type name
where name is the variable name, type is the type of the data it is supposed to hold. It is ‘string’ for string variables and ‘number’ for numeric ones.
For example, this is a declaration of a string variable ‘var’:
string var
If a variable declaration occurs within a function (see User-defined) or handler (see Handlers), it declares an automatic variable, local to this function or handler. Otherwise, it declares a global variable.
Optional qualifiers are allowed only in global declarations, i.e.
in the variable declarations that appear outside of functions. They
specify the scope of the variable. The public qualifier
declares the variable as public and the static qualifier
declares it as static. The default scope is ‘public’,
unless specified otherwise in the module declaration (see module structure).
Additionally, qualifiers may contain the word precious,
which instructs the compiler to mark this variable as precious.
(see precious variables). The value of the precious variable
is not affected by the SMTP ‘RSET’ command. If both
scope qualifier and precious are used, they may appear in any
order, e.g.:
static precious string rcpt_list
or
precious static string rcpt_list
Declaration can be followed by any valid MFL expression, which supplies the initial value or initializer for the variable, for example:
string var "test"
A variable declared without initializer is implicitly initialized to a null value, no matter what its scope: a numeric variable assumes initial value 0, a string variables is initialized to an empty string.
A variable is assigned a value using the set statement:
set name expr
where name is the variable name and expr is a
mailfromd expression (see Expressions). The effect of
this statement is that the expr is evaluated and the value it
yields is assigned to the variable name.
If the set statement is located outside a function or handler
definition, the expr must be a constant expression, i.e. the
compiler should be able to evaluate it immediately. See optimizer.
It is not an error to assign a value to a variable that is not declared. In this case the assignment first declares a global or automatic variable having the type of expr and then assigns a value to it. Automatic variable is created if the assignment occurs within a function or handler, global variable is declared if it occurs at topmost lexical level. This is called implicit variable declaration.
In the MFL program, variables are referenced by their name. When appearing inside a double-quoted string, variables are referenced using the notation ‘%name’. Any variable being referenced must have been declared earlier (either explicitly or implicitly).
Mailfromd Manual:
Several variables are predefined. In mailfromd version
8.14 these are:
This variable is set by stdpoll and strictpoll built-ins
(and, consequently, by the on poll statement). Its value is
‘1’ if the function used the cached data instead of directly
polling the host, and ‘0’ if the polling took place.
See SMTP Callout functions.
You can use this variable to make your reject message more informative
for the remote party. The common paradigm is to define a function,
returning empty string if the result was obtained from polling, or
some notice if cached data were used, and to use the function in the
reject text, for example:
func cachestr() returns string
do
if cache_used
return "[CACHED] "
else
return ""
fi
done
Then, in prog envfrom one can use:
on poll $f do when not_found or failure: reject 550 5.1.0 cachestr() . "Sender validity not confirmed" done
Name of virus identified by ClamAV. Set by clamav
function (see ClamAV).
Number of seconds left to the end of greylisting period. Set by
greylist and is_greylisted functions (see Special test functions).
Name of the domain used by polling functions in SMTP
EHLO or HELO command. Default value is the fully
qualified domain name of the host where mailfromd is run.
See Polling.
Callout functions (see SMTP Callout functions) set this variable before returning. It contains the initial SMTP reply from the last polled host.
Callout functions (see SMTP Callout functions) set this variable before
returning. It contains the reply to the HELO (EHLO)
command, received from the last polled host.
Callout functions (see SMTP Callout functions) set this variable before returning. It contains the host name or IP address of the last polled host.
Callout functions (see SMTP Callout functions) set this variable before returning. It contains the last SMTP reply received from the remote host. In case of multi-line replies, only the first line is stored. If nothing was received the variable contains the string ‘nothing’.
Callout functions (see SMTP Callout functions) set this variable before
returning. It contains the last SMTP command sent to the
polled host. If nothing was sent, last_poll_sent contains the string
‘nothing’.
Email address used by polling functions in SMTP MAIL
FROM command (see Polling.). Default is ‘<>’. Here is an
example of how to change it:
set mailfrom_address "postmaster@my.domain.com"
You can set this value to a comma-separated list of email addresses, in which case the probing will try each address until either the remote party accepts it or the list of addresses is exhausted, whichever happens first.
It is not necessary to enclose emails in angle brackets, as they will be added automatically where appropriate. The only exception is null return address, when used in a list of addresses. In this case, it should always be written as ‘<>’. For example:
set mailfrom_address "postmaster@my.domain.com, <>"
Spam score for the message, set by sa function (see sa).
The variable rcpt_count keeps the number of recipients given so
far by RCPT TO commands. It is defined only in ‘envrcpt’
handlers.
Spam threshold, set by sa function (see sa).
Spam keywords for the message, set by sa function (see sa).
This variable controls the verbosity of the exception-safe database functions. See safedb_verbose.
Mailfromd Manual:
A back reference is a sequence ‘\d’, where d
is a decimal number. It refers to the dth parenthesized
subexpression in the last matches statement13. Any back reference occurring within a
double-quoted string is replaced with the value of the corresponding
subexpression. For example:
if $f matches '.*@\(.*\)\.gnu\.org\.ua' set host \1 fi
If the value of f macro is ‘smith@unza.gnu.org.ua’, the
above code will assign the string ‘unza’ to the variable
host.
Notice, that each occurrence of matches will reset the table
of back references, so try to use them as early as possible. The
following example illustrates a common error, when the back
reference is used after the reference table has been reused by another
matching:
# Wrong!
if $f matches '.*@\(.*\)\.gnu\.org\.ua'
if $f matches 'some.*'
set host \1
fi
fi
This will produce the following run time error:
mailfromd: RUNTIME ERROR near file.mf:3: Invalid back-reference number
because the inner match (‘some.*’) does not have any parenthesized subexpressions.
See Special comparisons, for more information about matches
operator.
Mailfromd Manual:
Milter stage handler (or handler, for short) is a subroutine responsible for processing a particular milter state. There are eight handlers available. Their order of invocation and arguments are described in Figure 3.1.
A handler is defined using the following construct:
prog handler-name do handler-body done
where handler-name is the name of the handler (see handler names), handler-body is the list of filter statements composing the handler body. Some handlers take arguments, which can be accessed within the handler-body using the notation $n, where n is the ordinal number of the argument. Here we describe the available handlers and their arguments:
This handler is called once at the beginning of each SMTP connection.
string;
The host name of the message sender, as reported by MTA. Usually it
is determined by a reverse lookup on the host address. If the reverse
lookup fails, ‘$1’ will contain the message sender’s IP address
enclosed in square brackets (e.g. ‘[127.0.0.1]’).
number;
Socket address family. You need to require the ‘status’ module
to get symbolic definitions for the address families. Supported
families are:
| Constant | Value | Meaning |
|---|---|---|
| FAMILY_STDIO | 0 | Standard input/output (the MTA is run with -bs option) |
| FAMILY_UNIX | 1 | UNIX socket |
| FAMILY_INET | 2 | IPv4 protocol |
| FAMILY_INET6 | 3 | IPv6 protocol |
Table 4.3: Supported socket families
number;
Port number if ‘$2’ is ‘FAMILY_INET’.
string;
Remote IP address if ‘$2’ is ‘FAMILY_INET’ or full file name
of the socket if ‘$2’ is ‘FAMILY_UNIX’. If ‘$2’ is
‘FAMILY_STDIO’, ‘$4’ is an empty string.
The actions (see Actions) appearing in this handler
are handled by Sendmail in a special way. First of all, any textual
message is ignored. Secondly, the only action that immediately closes
the connection is tempfail 421. Any other reply codes result in
Sendmail switching to nullserver mode, where it accepts any
commands, but answers with a failure to any of them, except for the
following: QUIT, HELO, NOOP, which are processed
as usual.
The following table summarizes the Sendmail behavior depending on the action used:
tempfail 421 excode messageThe caller is returned the following error message:
421 4.7.0 hostname closing connection
Both excode and message are ignored.
tempfail 4xx excode message(where xx represents any digits, except ‘21’) Both excode and message are ignored. Sendmail switches to nullserver mode. Any subsequent command, excepting the ones listed above, is answered with
454 4.3.0 Please try again later
reject 5xx excode message(where xx represents any digits). All arguments are ignored. Sendmail switches to nullserver mode. Any subsequent command, excepting ones listed above, is answered with
550 5.0.0 Command rejected
Regarding reply codes, this behavior complies with RFC 2821 (section 3.9), which states:
An SMTP server must not intentionally close the connection except:
[…]
- After detecting the need to shut down the SMTP service and returning a 421 response code. This response code can be issued after the server receives any command or, if necessary, asynchronously from command receipt (on the assumption that the client will receive it after the next command is issued).
However, the RFC says nothing about textual messages and
extended error codes, therefore Sendmail’s ignoring of these is,
in my opinion, absurd. My practice shows that it is often reasonable,
and even necessary, to return a meaningful textual message if the
initial connection is declined. The opinion of mailfromd
users seems to support this view. Bearing this in mind,
mailfromd is shipped with a patch for Sendmail,
which makes it honor both extended return code and textual message given
with the action. Two versions are provided:
etc/sendmail-8.13.7.connect.diff, for
Sendmail versions 8.13.x, and
etc/sendmail-8.14.3.connect.diff, for Sendmail versions 8.14.3.
This handler is called whenever the SMTP client sends HELO or
EHLO command. Depending on the actual MTA configuration, it
can be called several times or even not at all.
string; Argument to HELO (EHLO) commands.
According to RFC 28221, $1 must be domain name of the
sending host, or, in case this is not available, its IP address
enclosed in square brackets. Be careful when taking decisions based
on this value, because in practice many hosts send arbitrary strings.
We recommend to use heloarg_test function
(see heloarg_test) if you wish to analyze this value.
Called when the SMTP client sends MAIL FROM command, i.e. once
at the beginning of each message.
string; First argument to the MAIL FROM command,
i.e. the email address of the sender.
string; Rest of arguments to MAIL FROM separated
by space character. This argument can be ‘""’.
$1 is not the same as $f Sendmail variable, because
the latter contains the sender email after address rewriting and
normalization, while $1 contains exactly the value given by
sending party.
$2 will contain
an array of arguments.
Called once for each RCPT TO command, i.e. once for each
recipient, immediately after envfrom.
string; First argument to the RCPT TO command,
i.e. the email address of the recipient.
string; Rest of arguments to RCPT TO separated
by space character. This argument can be ‘""’.
When the array type is implemented, $2 will contain
an array of arguments.
Called after the MTA receives SMTP ‘DATA’ command. Notice that this handler is not supported by Sendmail versions prior to 8.14.0 and Postfix versions prior to 2.5.
None
Called once for each header line received after SMTP DATA command.
string; Header field name.
string; Header field value. The content of the header may
include folded white space, i.e., multiple lines with following white
space where lines are separated by LF (ASCII 10). The
trailing line terminator (CR/LF) is removed.
This handler is called once per message, after all headers have been sent and processed.
None.
This header is called zero or more times, for each piece of the message body obtained from the remote host.
pointer; Piece of body text. See ‘Notes’ below.
number; Length of data pointed to by $1, in bytes.
The first argument points to the body chunk. Its size may be quite
considerable and passing it as a string may be costly both in terms of
memory and execution time. For this reason it is not passed as a
string, but rather as a generic pointer, i.e. an object having
the same size as number, which can be used to retrieve the
actual contents of the body chunk if the need arises.
A special function body_string is provided to convert this
object to a regular MFL string (see Mail body functions). Using it you can collect the entire body text into a
single global variable, as illustrated by the following example:
string text prog body do set text text . body_string($1,$2) done
The text collected this way can then be used in the eom handler
(see below) to parse and analyze it.
If you wish to analyze both the headers and mail body, the following code fragment will do that for you:
string text # Collect all headers. prog header do set text text . $1 . ": " . $2 . "\n" done # Append terminating newline to the headers. prog eoh do set text "%text\n" done # Collect message body. prog body do set text text . body_string($1, $2) done
This handler is called once per message, when the terminating dot
after DATA command has been received.
None
This handler is useful for calling message capturing functions,
such as sa or clamav. For more information about these,
refer to Interfaces to Third-Party Programs.
For your reference, the following table shows each handler with its arguments:
| Handler | $1 | $2 | $3 | $4 |
|---|---|---|---|---|
| connect | Hostname | Socket Family | Port | Remote address |
| helo | HELO domain | N/A | N/A | N/A |
| envfrom | Sender email address | Rest of arguments | N/A | N/A |
| envrcpt | Recipient email address | Rest of arguments | N/A | N/A |
| header | Header name | Header value | N/A | N/A |
| eoh | N/A | N/A | N/A | N/A |
| body | Body segment (pointer) | Length of the segment (numeric) | N/A | N/A |
| eom | N/A | N/A | N/A | N/A |
Table 4.4: State Handler Arguments
Mailfromd Manual:
Apart from the milter handlers described in the previous section, MFL defines two special handlers, called ‘begin’ and ‘end’, which supply startup and cleanup instructions for the filter program.
The ‘begin’ special handler is executed once for each SMTP session, after the connection has been established but before the first milter handler has been called. Similarly, the ‘end’ handler is executed exactly once, after the connection has been closed. Neither of them takes any arguments.
The two handlers are defined using the following syntax:
# Begin handler begin do … done # End handler end do … done
where ‘…’ represent any MFL statements.
An MFL program may have multiple ‘begin’ and ‘end’ definitions. They can be intermixed with other definitions. The compiler combines all ‘begin’ statements into a single one, in the order they appear in the sources. Similarly, all ‘end’ blocks are concatenated together. The resulting ‘begin’ is called once, at the beginning of each SMTP session, and ‘end’ is called once at its termination.
Multiple ‘begin’ and ‘end’ handlers are a useful feature
for writing modules (see Modules), because each module can thus
have its own initialization and cleanup blocks. Notice, however, that
in this case the order in which subsequent ‘begin’ and ‘end’
blocks are executed is not defined. It is only warranted that all
‘begin’ blocks are executed at startup and all ‘end’ blocks
are executed at shutdown. It is also warranted that all ‘begin’
and ‘end’ blocks defined within a compilation unit (i.e. a single
abstract source file, with all #include and
#include_once statements expanded in place) are executed in
order of their appearance in the unit.
Due to their special nature, the startup and cleanup blocks impose certain restrictions on the statements that can be used within them:
return cannot be used in ‘begin’ and ‘end’
handlers.
accept, continue, discard, reject,
tempfail. They can, however, be used in catch
statements, declared in ‘begin’ blocks (see example below).
The ‘begin’ handlers are the usual place to put global initialization code to. For example, if you do not want to use DNS caching, you can do it this way:
begin
do
db_set_active("dns", 0)
done
Additionally, you can set up global exception handling routines there. For example, the following ‘begin’ statement installs a handler for all exceptions not handled otherwise that logs the exception along with the stack trace and continues processing the message:
begin
do
catch *
do
echo "Caught exception $1: $2"
stack_trace()
continue
done
done
Mailfromd Manual:
A function is a named mailfromd subroutine, which
takes zero or more parameters and optionally returns a certain
value. Depending on the return value, functions can be
subdivided into string functions and number functions.
A function may have mandatory and optional parameters.
When invoked, the function must be supplied exactly as many
actual arguments as the number of its mandatory parameters.
Functions are invoked using the following syntax:
name (args)
where name is the function name and args is a comma-separated list of expressions. For example, the following are valid function calls:
foo(10)
interval("1 hour")
greylist("/var/my.db", 180)
The number of parameters a function takes and their data types compose the function signature. When actual arguments are passed to the function, they are converted to types of the corresponding formal parameters.
There are two major groups of functions: built-in functions,
that are implemented in the mailfromd binary, and
user-defined functions, that are written in MFL. The
invocation syntax is the same for both groups.
Mailfromd is shipped with a rich set of library
functions. These are described in Library. In addition to
these you can define your own functions.
Function definitions can appear anywhere between the handler declarations in a filter program, the only requirement being that the function definition occur before the place where the function is invoked.
The syntax of a function definition is:
[qualifier] func name (param-decl) returns data-type do function-body done
where name is the name of the function to define, param-decl is a comma-separated list of parameter declarations. The syntax of the latter is the same as that of variable declarations (see Variable declarations), i.e.:
type name
declares the parameter name having the type type. The
type is string or number.
Optional qualifier declares the scope of visibility for that function (see scope of visibility). It is similar to that of variables, except that functions cannot be local (i.e. you cannot declare function within another function).
The public qualifier declares a function that may be referred
to from any module, whereas the static qualifier declares a
function that may be called only from the current module
(see Modules). The default scope is ‘public’,
unless specified otherwise in the module declaration (see module structure).
For example, the following declares a function ‘sum’, that takes two numeric arguments and returns a numeric value:
func sum(number x, number y) returns number
Similarly, the following is a declaration of a static function:
static func sum(number x, number y) returns number
Parameters are referenced in the function-body by their name,
the same way as other variables. Similarly, the value of a parameter can be
altered using set statement.
A function can be declared to take a certain number of optional
arguments. In a function declaration, optional abstract arguments
must be placed after the mandatory ones, and must be separated from
them with a semicolon. The following example is a definition of
function foo, which takes two mandatory and two optional
arguments:
func foo(string msg, string email; number x, string pfx)
Mandatory parameters are: msg and email. Optional
parameters are: x and pfx. The actual number of
arguments supplied to the function is returned by a special construct
$#. In addition, the special construct @arg
evaluates to the ordinal number of variable arg in the list of
formal parameters (the first argument has number ‘0’). These two
constructs can be used to verify whether an argument is supplied to
the function.
When an actual argument for parameter n is supplied, the number
of actual arguments ($#) is greater than the ordinal number
of that parameter in the declaration list (@n). Thus,
the following construct can be used to check if an optional argument
arg is actually supplied:
func foo(string msg, string email; number x, string arg)
do
if $# > @arg
…
fi
The default mailfromd installation provides a special
macro for this purpose: see defined. Using it, the example above
could be rewritten as:
func foo(string msg, string email; number x, string arg)
do
if defined(arg)
…
fi
Within a function body, optional arguments are referenced exactly the same way as the mandatory ones. Attempt to dereference an optional argument for which no actual parameter was supplied, results in an undefined value, so be sure to check whether a parameter is passed before dereferencing it.
A function can also take variable number of arguments (such
functions are called variadic). This is
indicated by the use of ellipsis as the last abstract parameter. The
statement below defines a function foo taking one mandatory, one
optional and any number of additional arguments:
func foo (string a ; string b, ...)
All actual arguments passed in a list of variable arguments are coerced to string data type. To refer to these arguments in the function body, the following construct is used:
$(expr)
where expr is any valid MFL expression, evaluating to
a number n. This construct refers to the value of nth
actual parameter from the variable argument list. Parameters are
numbered from ‘1’, so the first variable parameter is $(1),
and the last one is $($# - Nm - No), where Nm
and No are numbers of mandatory and optional parameters to the
function.
The construct ‘$(n)’ where 1 <= n <= 9 can also be written as ‘$n’.
For example, the function below prints all its arguments:
func pargs (string text, ...)
do
echo "text=%text"
loop for number i 1,
while i < $# - @text,
set i i + 1
do
echo "arg %i=" . $(i)
done
done
Note how the ordinal number operator is used to compute the upper limit.
The function-body is any list of valid mailfromd
statements. In addition to the statements discussed below
(see Statements) it can also contain the return statement,
which is used to return a value from the function. The syntax of the
return statement is
return value
As an example of this, consider the following code snippet that defines the function ‘sum’ to return a sum of its two arguments:
func sum(number x, number y) returns number
do
return x + y
done
The returns part in the function declaration is optional. A
declaration lacking it defines a procedure, or void
function, i.e. a function that is not supposed to return any value.
Such functions cannot be used in expressions, instead they are
used as statements (see Statements). The following example
shows a function that emits a customized temporary failure notice:
func stdtf() do tempfail 451 4.3.5 "Try again later" done
A function may have several names. An alternative name (or
alias) can be assigned to a function by using alias
keyword, placed after param-decl part, for example:
func foo() alias bar returns string do … done
After this declaration, both foo() and bar() will refer
to the same function.
The number of function aliases is unlimited. The following fragment declares a function having three names:
func foo() alias bar alias baz returns string do … done
Although this feature is rarely needed, there are sometimes cases when it may be necessary.
A variable declared within a function becomes a local variable to
this function. Its lexical scope ends with the terminating
done statement.
Parameters, local variables and global variables are using separate namespaces, so a parameter name can coincide with the name of a global, in which case a parameter is said to shadow the global. All references to its name will refer to the parameter, until the end of its scope is reached, where the global one becomes visible again. Consider the following example:
number x
func foo(string x)
do
echo "foo: %x"
done
prog envfrom
do
set x "Global"
foo("Local")
echo x
done
Running mailfromd --test with this configuration will
display:
foo: Local Global |
Mailfromd Manual:
To illustrate the concept of user-defined functions, this subsection
shows the definitions of some of the library functions shipped with
mailfromd14.
These functions are contained in modules installed along with the
mailfromd binary. To use any of them in your code, require
the appropriate module as described in import, e.g. to use the
revip function, do require 'revip'.
Functions and their definitions:
revipThe function revip (see revip) is implemented as follows:
func revip(string ip) returns string do return inet_ntoa(ntohl(inet_aton(ip))) done
Previously it was implemented using regular expressions. Below we include this variant as well, as an illustration for the use of regular expressions:
#pragma regex push +extended
func revip(string ip) returns string
do
if ip matches '([0-9]+)\.([0-9]+)\.([0-9]+)\.([0-9]+)'
return "\4.\3.\2.\1"
fi
return ip
done
#pragma regex pop
strip_domain_partThis function returns at most n last components of the domain name domain (see strip_domain_part).
#pragma regex push +extended
func strip_domain_part(string domain, number n) returns string
do
if n > 0 and
domain matches '.*((\.[^.]+){' . $2 . '})'
return substring(\1, 1, -1)
else
return domain
fi
done
#pragma regex pop
valid_domainSee valid_domain, for a description of this function. Its definition follows:
require dns func valid_domain(string domain) returns number do return not (resolve(domain) = "0" and not hasmx(domain)) done
match_dnsblThe function match_dnsbl (see match_dnsbl) is defined as
follows:
require dns
require match_cidr
#pragma regex push +extended
func match_dnsbl(string address, string zone, string range)
returns number
do
string rbl_ip
if range = 'ANY'
set rbl_ip '127.0.0.0/8'
else
set rbl_ip range
if not range matches '^([0-9]{1,3}\.){3}[0-9]{1,3}$'
return 0
fi
fi
if not (address matches '^([0-9]{1,3}\.){3}[0-9]{1,3}$'
and address != range)
return 0
fi
if address matches
'^([0-9]{1,3})\.([0-9]{1,3})\.([0-9]{1,3})\.([0-9]{1,3})$'
if match_cidr (resolve ("\4.\3.\2.\1", zone), rbl_ip)
return 1
else
return 0
fi
fi
# never reached
done
Mailfromd Manual:
Expressions are language constructs, that evaluate to a value, that can subsequently be echoed, tested in a conditional statement, assigned to a variable or passed to a function.
Mailfromd Manual:
Literals and numbers are constant expressions. They evaluate to string and numeric types.
Mailfromd Manual:
A function call is an expression. Its type is the return type of the function.
Mailfromd Manual:
Concatenation operator is ‘.’ (a dot). For example, if
$f is ‘smith’, and $client_addr is
‘10.10.1.1’, then:
$f . "-" . $client_addr ⇒ "smith-10.10.1.1"
Any two adjacent literal strings are concatenated, producing a new string, e.g.
"GNU's" " not " "UNIX" ⇒ "GNU's not UNIX"
Mailfromd Manual:
The filter script language offers the common arithmetic operators: ‘+’, ‘-’, ‘*’ and ‘/’. In addition, the ‘%’ is a modulo operator, i.e. it computes the remainder of division of its operands.
All of them follow usual precedence rules and work as you would expect them to.
Mailfromd Manual:
The ‘<<’ represents a bitwise shift left operation, which shifts the binary representation of the operand on its left by the number of bits given by the operand on its right.
Similarly, the ‘>>’ represents a bitwise shift right.
Mailfromd Manual:
Relational expressions are:
| Expression | Result |
|---|---|
x < y | True if x is less than y. |
x <= y | True if x is less than or equal to y. |
x > y | True if x is greater than y. |
x >= y | True if x is greater than or equal to y. |
x = y | True if x is equal to y. |
x != y | True if x is not equal to y. |
Table 4.5: Relational Expressions
The relational expressions apply to string as well as to numbers. When a relational operation applies to strings, case-sensitive comparison is used, e.g.:
"String" = "string" ⇒ False "String" < "string" ⇒ True
Mailfromd Manual:
In addition to the traditional relational operators, described
above, mailfromd provides two operators for regular
expression matching:
| Expression | Result |
|---|---|
x matches y | True if the string x matches the regexp denoted by y. |
x fnmatches y | True if the string x matches the globbing pattern denoted by y. |
Table 4.6: Regular Expression Matching
The type of the regular expression used by matches operator
is controlled by #pragma regex (see pragma regex). For example:
$f ⇒ "gray@gnu.org.ua" $f matches '.*@gnu\.org\.ua' ⇒true$f matches '.*@GNU\.ORG\.UA' ⇒false#pragma regex +icase $f matches '.*@GNU\.ORG\.UA' ⇒true
The fnmatches operator compares its left-hand operand with a
globbing pattern (see glob(7)) given as its right-hand side
operand. For example:
$f ⇒ "gray@gnu.org.ua" $f fnmatches "*ua" ⇒true$f fnmatches "*org" ⇒false$f fnmatches "*org*" ⇒true
Both operators have a special form, for ‘MX’ pattern matching. The expression:
x mx matches y
is evaluated as follows: first, the expression x is analyzed and, if it is an email address, its domain part is selected. If it is not, its value is used verbatim. Then the list of ‘MX’s for this domain is looked up. Each of ‘MX’ names is then compared with the regular expression y. If any of the names matches, the expression returns true. Otherwise, its result is false.
Similarly, the expression:
x mx fnmatches y
returns true only if any of the ‘MX’s for (domain or email) x match the globbing pattern y.
Both mx matches and mx fnmatches can signal the
following exceptions: e_temp_failure, e_failure.
The value of any parenthesized subexpression occurring within the
right-hand side argument to matches or mx matches can be
referenced using the notation ‘\d’, where d is the
ordinal number of the subexpression (subexpressions are numbered from
left to right, starting at 1). This notation is allowed in the
program text as well as within double-quoted strings and
here-documents, for example:
if $f matches '.*@\(.*\)\.gnu\.org\.ua' set message "Your host name is \1;" fi
Remember that the grouping symbols are ‘\(’ and ‘\)’ for basic regular expressions, and ‘(’ and ‘)’ for extended regular expressions. Also make sure you properly escape all special characters (backslashes in particular) in double-quoted strings, or use single-quoted strings to avoid having to do so (see singe-vs-double, for a comparison of the two forms).
Mailfromd Manual:
A boolean expression is a combination of relational or
matching expressions using the boolean operators and, or
and not, and, eventually, parentheses to control nesting:
| Expression | Result |
|---|---|
x and y | True only if both x and y are true. |
x or y | True if any of x or y is true. |
not x | True if x is false. |
table 4.1: Boolean Operators
Binary boolean expressions are computed using shortcut evaluation:
x and yIf x ⇒ , the result is falsefalse
and y is not evaluated.
x or yIf x ⇒ , the result is truetrue and
y is not evaluated.
Mailfromd Manual:
Operator precedence is an abstract value associated with each
language operator, that determines the order in which operators are
executed when they appear together within a single expression.
Operators with higher precedence are executed first. For example,
‘*’ has a higher precedence than ‘+’, therefore the
expression a + b * c is evaluated in the following order: first
b is multiplied by c, then a is added to the
product.
When operators of equal precedence are used together they are evaluated from left to right (i.e., they are left-associative), except for comparison operators, which are non-associative (these are explicitly marked as such in the table below). This means that you cannot write:
if 5 <= x <= 10
Instead, you should write:
if 5 <= x and x <= 10
The precedence of the mailfromd operators where selected
so as to match that used in most programming languages.15
The following table lists all operators in order of decreasing precedence:
(...)Grouping
$ %Sendmail macros and mailfromd variables
* /Multiplication, division
+ -Addition, subtraction
<< >>Bitwise shift left and right
< <= >= >Relational operators (non-associative)
= != matches fnmatchesEquality and special comparison (non-associative)
&Logical (bitwise) AND
^Logical (bitwise) XOR
|Logical (bitwise) OR
notBoolean negation
andLogical ‘and’.
orLogical ‘or’
.String concatenation
Mailfromd Manual:
When two operands on each side of a binary expression have
different type, mailfromd evaluator coerces them to a
common type. This is known as implicit type casting. The rules
for implicit type casting are:
The construct for explicit type cast is:
type(expr)
where type is the name of the type to coerce expr to. For example:
string(2 + 4*8) ⇒ "34"
Mailfromd Manual:
When any two named entities happen to have the same name we say that a name clash occurs. The handling of name clashes depends on types of the entities involved in it.
A name of a constant or variable can coincide with that of a function, it does not produce any warnings or errors because functions, variables and constants use different namespaces. For example, the following code is correct:
const a 4 func a() do echo a done
When executed, it prints ‘4’.
Redefinition of a function or using a predefined handler name (see Handlers) as a function name results in a fatal error. For example, compiling this code:
func a() do echo "1" done func a() do echo "2" done
causes the following error message:
mailfromd: sample.mf:9: syntax error, unexpected FUNCTION_PROC, expecting IDENTIFIER
A variable name can coincide with a handler name. For example, the following code is perfectly OK:
string envfrom "M"
prog envfrom
do
echo envfrom
done
If two handlers with the same name are defined, the definition that appears further in the source text replaces the previous one. A warning message is issued, indicating locations of both definitions, e.g.:
mailfromd: sample.mf:116: Warning: Redefinition of handler `envfrom' mailfromd: sample.mf:34: Warning: This is the location of the previous definition
Defining a variable having the same name as an already defined one results in a warning message being displayed. The compilation succeeds. The second variable shadows the first, that is any subsequent references to the variable name will refer to the second variable. For example:
string x "Text" number x 1 prog envfrom do echo x done
Compiling this code results in the following diagnostics:
mailfromd: sample.mf:4: Redeclaring `x' as different data type mailfromd: sample.mf:2: This is the location of the previous definition
Executing it prints ‘1’, i.e. the value of the last definition of
x.
The scope of the shadowing depends on storage classes of the two variables. If both of them have external storage class (i.e. are global ones), the shadowing remains in effect until the end of input. In other words, the previous definition of the variable is effectively forgotten.
If the previous definition is a global, and the shadowing definition is an automatic variable or a function parameter, the scope of this shadowing ends with the scope of the second variable, after which the previous definition (global) becomes visible again. Consider the following code:
set x "initial"
func foo(string x) returns string
do
return x
done
prog envfrom
do
echo foo("param")
echo x
done
Its compilation produces the following warning:
mailfromd: sample.mf:3: Warning: Parameter `x' is shadowing a global
When executed, it produces the following output:
param initial State envfrom: continue
If a constant is defined which has the same name as a previously defined variable (the constant shadows the variable), the compiler prints the following diagnostic message:
file:line: Warning: Constant name `name' clashes with a variable name file:line: Warning: This is the location of the previous definition
A similar diagnostics is issued if a variable is defined whose name coincides with a previously defined constant (the variable shadows the constant).
In any case, any subsequent notation %name refers to the last defined symbol, be it variable or constant.
Notice, that shadowing occurs only when using %name notation. Referring to the constant using its name without ‘%’ allows to avoid shadowing effects.
If a variable shadows a constant, the scope of the shadowing depends
on the storage class of the variable. For automatic variables and
function parameters, it ends with the final done closing the
function. For global variables, it lasts up to the end of input.
For example, consider the following code:
const a 4 func foo(string a) do echo a done prog envfrom do foo(10) echo a done
When run, it produces the following output:
$ mailfromd --test sample.mf mailfromd: sample.mf:3: Warning: Variable name `a' clashes with a constant name mailfromd: sample.mf:1: Warning: This is the location of the previous definition 10 4 State envfrom: continue
Redefining a constant produces a warning message. The latter definition shadows the former. Shadowing remains in effect until the end of input.
Mailfromd Manual:
Statements are language constructs, that, unlike expressions, do not return any value. Statements execute some actions, such as assigning a value to a variable, or serve to control the execution flow in the program.
Mailfromd Manual:
An action statement instructs mailfromd to
perform a certain action over the message being processed. There are
two kinds of actions: return actions and header manipulation actions.
Reply actions tell Sendmail to return given response code
to the remote party. There are five such actions:
acceptReturn an accept reply. The remote party will continue
transmitting its message.
reject code excode message-exprreject (code-expr, excode-expr, message-expr)Return a reject reply. The remote party will have to
cancel transmitting its message. The three arguments are optional,
their usage is described below.
tempfail code excode messagetempfail (code-expr, excode-expr, message-expr)Return a ‘temporary failure’ reply. The remote party can retry to send its message later. The three arguments are optional, their usage is described below.
discardInstructs Sendmail to accept the message and silently discard
it without delivering it to any recipient.
continueStops the current handler and instructs Sendmail to
continue processing of the message.
Two actions, reject and tempfail can take up to three
optional parameters. There are two forms of supplying these
parameters.
In the first form, called literal or traditional notation,
the arguments are supplied as additional words after the action name,
and are separated by whitespace. The first argument is a three-digit
RFC 2821 reply code. It must begin with ‘5’ for
reject and with ‘4’ for tempfail. If two arguments
are supplied, the second argument must be either an extended
reply code (RFC 1893/2034) or a textual string to be
returned along with the SMTP reply. Finally, if all three
arguments are supplied, then the second one must be an extended reply
code and the third one must give the textual string. The following
examples illustrate the possible ways of using the reject
statement:
reject reject 503 reject 503 5.0.0 reject 503 "Need HELO command" reject 503 5.0.0 "Need HELO command"
The notion textual string, used above means either a literal string or an MFL expression that evaluates to string. However, both code and extended code must always be literal.
The second form of supplying arguments is called functional notation, because it resembles the function syntax. When used in this form, the action word is followed by a parenthesized group of exactly three arguments, separated by commas. Each argument is a MFL expression. The meaning and ordering of the arguments is the same as in literal form. Any or all of these three arguments may be absent, in which case it will be replaced by the default value. To illustrate this, here are the statements from the previous example, written in functional notation:
reject(,,) reject(503,,) reject(503, 5.0.0) reject(503, , "Need HELO command") reject(503, 5.0.0, "Need HELO command")
Notice that there is an important difference between the two notations. The functional notation allows to compute both reply codes at run time, e.g.:
reject(500 + dig2*10 + dig3, "5.%edig2.%edig2")
Header manipulation actions provide basic means to add, delete or modify the message RFC 2822 headers.
add name stringAdd the header name with the value string. E.g.:
add "X-Seen-By" "Mailfromd 8.14"
(notice argument quoting)
replace name stringThe same as add, but if the header name already
exists, it will be removed first, for example:
replace "X-Last-Processor" "Mailfromd 8.14"
delete nameDelete the header named name:
delete "X-Envelope-Date"
These actions impose some restrictions. First of all, their first argument must be a literal string (not a variable or expression). Secondly, there is no way to select a particular header instance to delete or replace, which may be necessary to properly handle multiple headers (e.g. ‘Received’). For more elaborate ways of header modifications, see Header modification functions.
Mailfromd Manual:
An assignment is a special statement that assigns a value to the variable. It has the following syntax:
set name value
where name is the variable name and value is the value to be assigned to it.
Assignment statements can appear in any part of a filter program.
If an assignment occurs outside of function or handler definition,
the value must be a literal value (see Literals). If it
occurs within a function or handler definition, value can be any
valid mailfromd expression (see Expressions). In this
case, the expression will be evaluated and its value will be assigned
to the variable. For example:
set delay 150 prog envfrom do set delay delay * 2 … done
Mailfromd Manual:
pass statementThe pass statement has no effect. It is used in places
where no statement is needed, but the language syntax requires one:
on poll $f do when success: pass when not_found or failure: reject 550 done
Mailfromd Manual:
echo statementThe echo statement concatenates all its arguments into a single
string and sends it to the syslog using the priority
‘info’. It is useful for debugging your script, in
conjunction with built-in constants (see Built-in constants), for
example:
func foo(number x) do echo "%__file__:%__line__: foo called with arg %x" … done
Mailfromd Manual:
Conditional expressions, or conditionals for short, test some conditions and alter the control flow depending on the result. There are two kinds of conditional statements: if-else branches and switch statements.
The syntax of an if-else branching construct is:
if condition then-body [else else-body] fi
Here, condition is an expression that governs control flow
within the statement. Both then-body and else-body are
lists of mailfromd statements. If condition is
true, then-body is executed, if it is false, else-body is
executed. The ‘else’ part of the statement is optional. The
condition is considered false if it evaluates to zero, otherwise it is
considered true. For example:
if $f = "" accept else reject fi
This will accept the message if the value of the Sendmail
macro $f is an empty string, and reject it otherwise. Both
then-body and else-body can be compound statements
including other if statements. Nesting level of
conditional statements is not limited.
To facilitate writing complex conditional statements, the elif
keyword can be used to introduce alternative conditions, for example:
if $f = "" accept elif $f = "root" echo "Mail from root!" else reject fi
Another type of branching instruction is switch statement:
switch condition do case x1 [or x2 …]: stmt1 case y1 [or y2 …]: stmt2 . . . [default: stmt] done
Here, x1, x2, y1, y2 are literal expressions;
stmt1, stmt2 and stmt are arbitrary
mailfromd statements (possibly compound); condition is
the controlling expression. The vertical dotted row represent another
eventual ‘case’ branches.
This statement is executed as follows: the condition
expression is evaluated and if its value equals x1 or x2
(or any other x from the first case), then
stmt1 is executed. Otherwise, if condition evaluates
to y1 or y2 (or any other y from the second
case), then stmt2 is executed. Other case
branches are tried in turn. If none of them matches, stmt
(called the default branch) is executed.
There can be as many case branches as you wish. The
default branch is optional. There can be at most one
default branch.
An example of switch statement follows:
switch x do case 1 or 3: add "X-Branch" "1" accept case 2 or 4 or 6: add "X-Branch" "2" default: reject done
If the value of mailfromd variable x is 2 or 3,
it will accept the message immediately, and add a ‘X-Branch: 1’
header to it. If x equals 2 or 4 or 6, this code will add
‘X-Branch: 2’ header to the message and will continue processing
it. Otherwise, it will reject the message.
The controlling condition of a switch statement may evaluate
to numeric or string type. The type of the condition governs the
type of comparisons used in case branches: for numeric types,
numeric equality will be used, whereas for string types, string
equality is used.
Mailfromd Manual:
The loop statement allows for repeated execution of a block of code, controlled by some conditional expression. It has the following form:
loop [label]
[for stmt1] [,while expr1] [,stmt2]
do
stmt3
done [while expr2]
where stmt1, stmt2, and stmt3 are statement lists, expr1 and expr2 are expressions.
The control flow is as follows:
Thus, stmt3 is executed until either expr1 or expr2 yield a zero value.
The loop body – stmt3 – can contain special statements:
break [label]Terminates the loop immediately. Control passes to ‘6’ (End) in the formal definition above. If label is supplied, the statement terminates the loop statement marked with that label. This allows to break from nested loops.
It is similar to break statement in C or shell.
next [label]Initiates next iteration of the loop. Control passes to ‘4’ in the formal definition above. If label is supplied, the statement starts next iteration of the loop statement marked with that label. This allows to request next iteration of an upper-level loop from a nested loop statement.
The loop statement can be used to create iterative statements
of arbitrary complexity. Let’s illustrate it in comparison with C.
The statement:
loop do stmt-list done
creates an infinite loop. The only way to exit from such a loop is to
call break (or return, if used within a function),
somewhere in stmt-list.
The following statement is equivalent to while (expr1)
stmt-list in C:
loop while expr do stmt-list done
The C construct for (expr1; expr2; expr3)
is written in MFL as follows:
loop for stmt1, while expr2, stmt2 do stmt3 done
For example, to repeat stmt3 10 times:
loop for set i 0, while i < 10, set i i + 1 do stmt3 done
Finally, the C ‘do’ loop is implemented as follows:
loop do stmt-list done while expr
As a real-life example of a loop statement, let’s consider the
implementation of function ptr_validate, which takes a single
argument ipstr, and checks its validity using the following algorithm:
Perform a DNS reverse-mapping for ipstr, looking up the
corresponding PTR record in ‘in-addr.arpa’. For each record
returned, look up its IP addresses (A records). If ipstr is
among the returned IP addresses, return 1 (true), otherwise
return 0 (false).
The implementation of this function in MFL is:
#pragma regex push +extended
func ptr_validate(string ipstr) returns number
do
loop for string names dns_getname(ipstr) . " "
number i index(names, " "),
while i != -1,
set names substr(names, i + 1)
set i index(names, " ")
do
loop for string addrs dns_getaddr(substr(names, 0, i)) . " "
number j index(addrs, " "),
while j != -1,
set addrs substr(addrs, j + 1)
set j index(addrs, " ")
do
if ipstr == substr(addrs, 0, j)
return 1
fi
done
done
return 0
done
Mailfromd Manual:
When the running program encounters a condition it is not able to handle, it signals an exception. To illustrate the concept, let’s consider the execution of the following code fragment:
if primitive_hasmx(domainpart($f))
accept
fi
The function primitive_hasmx (see primitive_hasmx) tests whether the
domain name given as its argument has any ‘MX’ records. It should
return a boolean value. However, when querying the Domain Name
System, it may fail to get a definite result. For example, the DNS
server can be down or temporary unavailable. In other words,
primitive_hasmx can be in a situation when, instead of returning
‘yes’ or ‘no’, it has to return ‘don't know’. It has
no way of doing so, therefore it signals an exception.
Each exception is identified by exception type, an integer number associated with it.
Mailfromd Manual:
The first 21 exception numbers are reserved for
built-in exceptions. These are declared in module status.mf.
The following table summarizes all built-in exception types implemented by
mailfromd version 8.14. Exceptions are listed in
lexicographic order.
The called function cannot finish its task because an uncompatible message modification function was called at some point before it. For details, MMQ and dkim_sign.
General database failure. For example, the database cannot be opened. This exception can be signaled by any function that queries any DBM database.
Division by zero.
This exception is emitted by dbinsert built-in if the
requested key is already present in the database (see dbinsert).
Function reached end of file while reading. See I/O functions, for a description of functions that can signal this exception.
A general failure has occurred. In particular, this exception is
signaled by DNS lookup functions when any permanent failure occurs.
This exception can be signaled by any DNS-related function
(hasmx, poll, etc.) or operation (mx matches).
Invalid input format. This exception is signaled if input data to a
function are improperly formatted. In version 8.14 it is
signaled by message_burst function if its input message is not
formatted according to RFC 934. See Message digest functions.
Illegal byte sequence. Signaled when a string cannot be converted between character sets because a sequence of bytes was encountered that is not defined for the source character set or cannot be represented in the destination character set.
See MIME decoding, for details.
Invalid CIDR notation. This is signaled by
match_cidr function when its second argument is not a valid
CIDR.
Invalid IP address. This is signaled by match_cidr function
when its first argument is not a valid IP address.
Invalid time interval specification. It is signaled by
interval function if its argument is not a valid time interval
(see time interval specification).
An error occurred during the input-output operation. See I/O functions, for a description of functions that can signal this exception.
A Sendmail macro is undefined.
The argument of a DNS-related function cannot be resolved to host
name or IP address. Currently only ismx (see ismx) raises
this exception.
The supplied argument is outside the allowed range. This is
signalled, for example, by substring function (see substring).
Regular expression cannot be compiled. This can happen when a
regular expression (a right-hand argument of a matches
operator) is built at the runtime and the produced string is an
invalid regex.
String-to-number conversion failed. This can be signaled when a string is used in numeric context which cannot be converted to the numeric data type. For example:
set x "10a" if x / 2 …
The if condition will signal ston_conv, since ‘10a’
cannot be converted to a number.
A temporary failure has occurred. This can be signaled by DNS-related functions or operations.
The supplied URL is invalid. See Interfaces to Third-Party Programs.
In addition to these, two symbols are defined that are not exception
types in the strict sense of the world, but are provided to make
writing filter scripts more convenient. These are success,
meaning successful return from a function, and not_found,
meaning that the required entity (e.g. domain name or email address)
was not found. See Figure 4.1, for an illustration on
how these can be used. For consistency with other exception codes,
these can be spelled as e_success and e_not_found.
Mailfromd Manual:
You can define your own exception types using the dclex
statement:
dclex type
In this statement, type must be a valid MFL
identifier, not used for another constant (see Constants).
The dclex statement defines a new exception identified by
the constant type and allocates a new exception number for it.
The type can subsequently be used in throw and
catch statements, for example:
dclex myrange
number fact(number val)
returns number
do
if val < 0
throw myrange "fact argument is out of range"
fi
…
done
Mailfromd Manual:
Normally when an exception is signalled, the program execution is
terminated and the MTA is returned a tempfail
status. Additional information regarding the exception is then output
to the logging channel (see Logging and Debugging). However, the
user can intercept any exception by installing his own
exception-handling routines.
An exception-handling routine is introduced by a try–catch statement, which has the following syntax:
try do stmtlist done catch exception-list do handler-body done
where stmtlist and handler-body are sequences of
MFL statements and exception-list is the list of
exception types, separated by the word or. A special
exception-list ‘*’ is allowed and means all exceptions.
This construct works as follows. First, the statements from stmtlist are executed. If the execution finishes successfully, control is passed to the first statement after the ‘catch’ block. Otherwise, if an exception is signalled and this exception is listed in exception-list, the execution is passed to the handler-body. If the exception is not listed in exception-list, it is handled as usual.
The following example shows a ‘try--catch’ construct used for
handling eventual exceptions, signalled by primitive_hasmx.
try
do
if primitive_hasmx(domainpart($f))
accept
else
reject
fi
done
catch e_failure or e_temp_failure
do
echo "primitive_hasmx failed"
continue
done
The ‘try--catch’ statement can appear anywhere inside a function or a handler, but it cannot appear outside of them. It can also be nested within another ‘try--catch’, in either of its parts. Upon exit from a function or milter handler, all exceptions are restored to the state they had when it has been entered.
A catch block can also be used alone, without preceding try
part. Such a construct is called a standalone catch. It is
mostly useful for setting global exception handlers in a begin
statement (see begin/end). When used within a usual function or
handler, the exception handlers set by a standalone catch
remain in force until either another standalone catch appears further
in the same function or handler, or an end of the function is
encountered, whichever occurs first.
A standalone catch defined within a function must return from
it by executing return statement. If it does not do that
explicitly, the default value of 1 is returned. A standalone catch
defined within a milter handler must end execution with any of the
following actions: accept, continue, discard,
reject, tempfail. By default, continue is
used.
It is not recommended to mix ‘try--catch’ constructs and standalone catches. If a standalone catch appears within a ‘try--catch’ statement, its scope of visibility is undefined.
Upon entry to a handler-body, two implicit positional arguments
are defined, which can be referenced in handler-body as $1
and $2. The first argument gives the numeric code of the
exception that has occurred. The second argument is a textual string
containing a human-readable description of the exception.
The following is an improved version of the previous example, which uses these parameters to supply more information about the failure:
try
do
if primitive_hasmx(domainpart($f))
accept
else
reject
fi
done
catch e_failure or e_temp_failure
do
echo "Caught exception $1: $2"
continue
done
The following example defines the function hasmx that
returns true if the domain part of its argument has any ‘MX’ records, and
false if it does not or if an exception occurs 16.
func hasmx (string s)
returns number
do
try
do
return primitive_hasmx(domainpart(s))
done
catch *
do
return 0
done
done
The same function can written using standalone catch:
func hasmx (string s)
returns number
do
catch *
do
return 0
done
return primitive_hasmx(domainpart(s))
done
All variables remain visible within catch body, with the
exception of positional arguments of the enclosing handler. To access
positional arguments of a handler from the catch body, assign
them to local variables prior to the ‘try--catch’ construct, e.g.:
prog header
do
string hname $1
string hvalue $2
try
do
…
done
catch *
do
echo "Exception $1 while processing header %hname: %hvalue"
echo $2
tempfail
done
You can also generate (or raise) exceptions explicitly in the
code, using throw statement:
throw excode descr
The arguments correspond exactly to the positional parameters of the
catch statement: excode gives the numeric code of the
exception, descr gives its textual description. This statement
can be used in complex scripts to create non-local exits from deeply
nested statements.
Notice, that the the excode argument must be an immediate
value: an exception identifier (either a built-in one or one declared
previously using a dclex statement).
Mailfromd Manual:
The filter script language provides a wide variety of functions for
sender address verification or polling, for short. These
functions, which were described in SMTP Callout functions, can be
used to implement any sender verification method. The additional data
that can be needed is normally supplied by two global variables:
ehlo_domain, keeping the default domain for the EHLO
command, and mailfrom_address, which stores the sender address
for probe messages (see Predefined variables).
For example, a simplest way to implement standard polling would be:
prog envfrom
do
if stdpoll($1, ehlo_domain, mailfrom_address) == 0
accept
else
reject 550 5.1.0 "Sender validity not confirmed"
fi
done
However, this does not take into account exceptions that
stdpoll can signal. To handle them, one will have to use
catch, for example thus:
require status
prog envfrom
do
try
do
if stdpoll($1, ehlo_domain, mailfrom_address) == 0
accept
else
reject 550 5.1.0 "Sender validity not confirmed"
fi
done
catch e_failure or e_temp_failure
do
switch $1
do
case failure:
reject 550 5.1.0 "Sender validity not confirmed"
case temp_failure:
tempfail 450 4.1.0 "Try again later"
done
done
done
If polls are used often, one can define a wrapper function, and use it instead. The following example illustrates this approach:
func poll_wrapper(string email) returns number
do
catch e_failure or e_temp_failure
do
return email
done
return stdpoll(email, ehlo_domain, mailfrom_address)
done
prog envfrom
do
switch poll_wrapper($f)
do
case success:
accept
case not_found or failure:
reject 550 5.1.0 "Sender validity not confirmed"
case temp_failure:
tempfail 450 4.1.0 "Try again later"
done
done
Figure 4.1: Building Poll Wrappers
Notice the way envfrom handles success and
not_found, which are not exceptions in the strict sense of the
word.
The above paradigm is so common that mailfromd provides a
special language construct to simplify it: the on statement.
Instead of manually writing the wrapper function and using it as a
switch condition, you can rewrite the above example as:
prog envfrom
do
on stdpoll($1, ehlo_domain, mailfrom_address)
do
when success:
accept
when not_found or failure:
reject 550 5.1.0 "Sender validity not confirmed"
when temp_failure:
tempfail 450 4.1.0 "Try again later"
done
done
Figure 4.2: Standard poll example
As you see the statement is pretty similar to switch. The
major syntactic difference is the use of the keyword when to
introduce conditional branches.
General syntax of the on statement is:
on condition
do
when x1 [or x2 …]:
stmt1
when y1 [or y2 …]:
stmt2
.
.
.
done
The condition is either a function call or a special poll
statement (see below). The values used in when branches are
normally symbolic exception names (see exception names).
When the compiler processes the on statement it does the
following:
when branches; To avoid name clashes with
the user-defined functions, the wrapper name begins and ends with
‘$’ which normally is not allowed in the identifiers;
on body to the corresponding switch
statement;
A special form of the condition is poll keyword,
whose syntax is:
poll [for] email
[host host]
[from domain]
[as email]
The order of particular keywords in the poll statement is
arbitrary, for example as email can appear before
email as well as after it.
The simplest form, poll email, performs the standard
sender verification of email address email. It is translated
to the following function call:
stdpoll(email, ehlo_domain, mailfrom_address)
The construct poll email host host, runs the
strict sender verification of address email on the given host.
It is translated to the following call:
strictpoll(host, email, ehlo_domain, mailfrom_address)
Other keywords of the poll statement modify these two basic
forms. The as keyword introduces the email address to be used
in the SMTP MAIL FROM command, instead of
mailfrom_address. The from keyword sets the domain
name to be used in EHLO command. So, for example the following
construct:
poll email host host from domain as addr
is translated to
strictpoll(host, email, domain, addr)
To summarize the above, the code described in Figure 4.2 can be written as:
prog envfrom
do
on poll $f do
when success:
accept
when not_found or failure:
reject 550 5.1.0 "Sender validity not confirmed"
when temp_failure:
tempfail 450 4.1.0 "Try again later"
done
done
Mailfromd Manual:
A module is a logically isolated part of code that implements a separate concern or feature and contains a collection of conceptually united functions and/or data. Each module occupies a separate compilation unit (i.e. file). The functionality provided by a module is incorporated into another module or the main program by requiring this module or by importing the desired components from it.
Mailfromd Manual:
A module file must begin with a module declaration:
module modname [interface-type].
Note the final dot.
The modname parameter declares the name of the module. It is recommended that it be the same as the file name without the ‘.mf’ extension. The module name must be a valid MFL literal. It also must not coincide with any defined MFL symbol, therefore we recommend to always quote it (see example below).
The optional parameter interface-type defines the default scope of visibility for the symbols declared in this module. If it is ‘public’, then all symbols declared in this module are made public (importable) by default, unless explicitly declared otherwise (see scope of visibility). If it is ‘static’, then all symbols, not explicitly marked as public, become static. If the interface-type is not given, ‘public’ is assumed.
The actual MFL code follows the ‘module’ line.
The module definition is terminated by the logical end of its
compilation unit, i.e. either by the end of file, or by the
keyword bye, whichever occurs first.
Special keyword bye may be used to prematurely end the current
compilation unit before the physical end of the containing file.
Any material between bye and the end of file is ignored by the
compiler.
Let’s illustrate these concepts by writing a module ‘revip’:
module 'revip' public. func revip(string ip) returns string do return inet_ntoa(ntohl(inet_aton(ip))) done bye This text is ignored. You may put any additional documentation here.
Mailfromd Manual:
Scope of Visibility of a symbol defines from where this symbol may be referred to. Symbols in MFL may have either of the following two scopes:
Public symbols are visible from the current module, as well as from any external modules, including the main script file, provided that they are properly imported (see import).
Static symbols are visible only from the current module. There is no way to refer to them from outside.
The default scope of visibility for all symbols declared within
a module is defined in the module declaration (see module structure). It may be overridden for any individual symbol by
prefixing its declaration with an appropriate qualifier: either
public or static.
Mailfromd Manual:
Functions or variables declared in another module must be imported prior to their actual use. MFL provides two ways of doing so: by requiring the entire module or by importing selected symbols from it.
The require statement instructs the compiler to locate the
module modname and to load all public interfaces from it.
The compiler looks for the file modname.mf in the current search path (see include search path). If no such file is found, a compilation error is reported.
For example, the following statement:
require revip
imports all interfaces from the module revip.mf.
Another, more sophisticated way to import from a module is to use the ‘from ... import’ construct:
from module import symbols.
Note the final dot. The ‘from’ and ‘module’ statements are the only two constructs in MFL that require the delimiter.
The module has the same semantics as in the require
construct. The symbols is a comma-separated list of symbol
names to import from module. A symbol name may be given in
several forms:
Literals specify exact symbol names to import. For example, the following statement imports from module A.mf symbols ‘foo’ and ‘bar’:
from A import foo,bar.
Regular expressions must be surrounded by slashes. A regular expression instructs the compiler to import all symbols whose names match that expression. For example, the following statement imports from A.mf all symbols whose names begin with ‘foo’ and contain at least one digit after it:
from A import '/^foo.*[0-9]/'.
The type of regular expressions used in the ‘from’ statement is
controlled by #pragma regex (see regex).
Regular expression may be followed by a s-expression, i.e. a
sed-like expression of the form:
s/regexp/replace/[flags]
where regexp is a regular expression, replace is a replacement for each part of the input that matches regexp. S-expressions and their parts are discussed in detail in s-expression.
The effect of such construct is to import all symbols that match the regular expression and apply the s-expression to their names.
For example:
from A import '/^foo.*[0-9]/s/.*/my_&/'.
This statement imports all symbols whose names begin with ‘foo’ and contain at least one digit after it, and renames them, by prefixing their names with the string ‘my_’. Thus, if A.mf declared a function ‘foo_1’, it becomes visible under the name of ‘my_foo_1’.
Mailfromd Manual:
Before compiling the script file, mailfromd preprocesses
it. The built-in preprocessor handles only file inclusion
(see include), while the rest of traditional facilities, such as
macro expansion, are supported via m4, which is used as an
external preprocessor.
The detailed description of m4 facilities lies far beyond
the scope of this document. You will find a complete user manual in
GNU M4 in GNU M4 macro processor. For the
rest of this section we assume the reader is sufficiently
acquainted with m4 macro processor.
The external preprocessor is invoked with -s flag, instructing
it to include line synchronization information in its output, which
is subsequently used by MFL compiler for purposes of error
reporting. The initial set of macro definitions is supplied in file
pp-setup, located in the library search path17,
which is fed to the preprocessor input before the script file itself.
The default pp-setup file renames all m4 built-in
macro names so they all start with the prefix ‘m4_’18. It changes comment characters to ‘/*’, ‘*/’ pair,
and leaves the default quoting characters, grave (‘`’) and acute
(‘'’) accents without change. Finally, pp-setup defines the
following macros:
The identifier must be the name of an optional abstract
argument to the function. This macro must be used only within a function
definition. It expands to the MFL expression that yields
true if the actual parameter is supplied for identifier.
For example:
func rcut(string text; number num)
returns string
do
if (defined(num))
return substr(text, length(text) - num)
else
return text
fi
done
This function will return last num characters of text if num is supplied, and entire text otherwise, e.g.:
rcut("text string") ⇒ "text string"
rcut("text string", 3) ⇒ "ing"
Invoking the defined macro with the name of a mandatory argument
yields true
Provides a printf statement, that formats its optional
parameters in accordance with format and sends the resulting
string to the current log output (see Logging and Debugging).
See String formatting, for a description of format.
Example usage:
printf('Function %s returned %d', funcname, retcode)
A convenience macro. Expands to a call to gettext (see NLS Functions).
This macro intends to compensate for the lack of array data type in MFL. It splits the string list into segments delimited by string delim. For each segment, the MFL code code is executed. The code can use the variable var to refer to the segment string.
For example, the following fragment prints names of all existing
directories listed in the PATH environment variable:
string path getenv("PATH")
string seg
string_list_iterate(path, ":", seg, `
if access(seg, F_OK)
echo "%seg exists"
fi')
Care should be taken to properly quote its arguments. In the code
below the string str is treated as a comma-separated list of
values. To avoid interpreting the comma as argument delimiter the
second argument must be quoted:
string_list_iterate(str, `","', seg, `
echo "next segment: " . seg')
A convenience macro, that expands to msgid verbatim. It is
intended to mark the literal strings that should appear in the
.po file, where actual call to gettext (see NLS Functions) cannot be used. For example:
/* Mark the variable for translation: cannot use gettext here */
string message N_("Mail accepted")
prog envfrom
do
…
/* Translate and log the message */
echo gettext(message)
You can obtain the preprocessed output, without starting actual compilation, using -E command line option:
$ mailfromd -E file.mf
The output is in the form of preprocessed source code, which is sent to the standard output. This can be useful, among others, to debug your own macro definitions.
Macro definitions and deletions can be made on the command line, by using the -D and -U options. They have the following format:
Define a symbol name to have a value value. If
value is not supplied, the value is taken to be the empty
string. The value can be any string, and the macro can be
defined to take arguments, just as if it was defined from within the
input using the m4_define statement.
For example, the following invocation defines symbol COMPAT to
have a value 43:
$ mailfromd -DCOMPAT=43
A counterpart of the -D option is the option -U
(--undefine). It undefines a preprocessor symbol whose name
is given as its argument. The following example undefines the symbol
COMPAT:
$ mailfromd -UCOMPAT
The following two options are supplied mainly for debugging purposes:
Disables the external preprocessor.
Use command as external preprocessor. Be especially careful
with this option, because mailfromd cannot verify whether
command is actually some kind of a preprocessor or not.
Mailfromd Manual:
In this section we will discuss a working example of the filter script file. For the ease of illustration, it is divided in several sections. Each section is prefaced with a comment explaining its function.
This filter assumes that the mailfromd.conf file contains the following:
relayed-domain-file (/etc/mail/sendmail.cw,
/etc/mail/relay-domains);
io-timeout 33;
database cache {
negative-expire-interval 1 day;
positive-expire-interval 2 weeks;
};
Of course, the exact parameter settings may vary, what is important
is that they be declared. See Mailfromd Configuration, for a
description of mailfromd configuration file syntax.
Now, let’s return to the script. Its first part defines the configuration settings for this host:
#pragma regex +extended +icase set mailfrom_address "<>" set ehlo_domain "gnu.org.ua"
The second part loads the necessary source modules:
require 'status' require 'dns' require 'rateok'
Next we define envfrom handler. In the first two rules, it
accepts all mails coming from the null address and from the machines
which we relay:
prog envfrom
do
if $f = ""
accept
elif relayed hostname($client_addr)
accept
elif hostname($client_addr) = $client_addr
reject 550 5.7.7 "IP address does not resolve"
Next rule rejects all messages coming from hosts with dynamic IP addresses. A regular expression used to catch such hosts is not 100% fail-proof, but it tries to cover most existing host naming patterns:
elif hostname($client_addr) matches
".*(adsl|sdsl|hdsl|ldsl|xdsl|dialin|dialup|\
ppp|dhcp|dynamic|[-.]cpe[-.]).*"
reject 550 5.7.1 "Use your SMTP relay"
Messages coming from the machines whose host names contain something similar to an IP are subject to strict checking:
elif hostname($client_addr) matches
".*[0-9]{1,3}[-.][0-9]{1,3}[-.][0-9]{1,3}[-.][0-9]{1,3}.*"
on poll host $client_addr for $f do
when success:
pass
when not_found or failure:
reject 550 5.1.0 "Sender validity not confirmed"
when temp_failure:
tempfail
done
If the sender domain is relayed by any of the ‘yahoo.com’
or ‘nameserver.com’ ‘MX’s, no checks are performed. We
will greylist this message in envrcpt handler:
elif $f mx fnmatches "*.yahoo.com"
or $f mx fnmatches "*.namaeserver.com"
pass
Finally, if the message does not meet any of the above conditions, it is verified by the standard procedure:
else
on poll $f do
when success:
pass
when not_found or failure:
reject 550 5.1.0 "Sender validity not confirmed"
when temp_failure:
tempfail
done
fi
At the end of the handler we check if the sender-client pair does not exceed allowed mail sending rate:
if not rateok("$f-$client_addr", interval("1 hour 30 minutes"), 100)
tempfail 450 4.7.0 "Mail sending rate exceeded. Try again later"
fi
done
Next part defines the envrcpt handler. Its primary purpose
is to greylist messages from some domains that could not be checked
otherwise:
prog envrcpt
do
set gltime 300
if $f mx fnmatches "*.yahoo.com"
or $f mx fnmatches "*.namaeserver.com"
and not dbmap("/var/run/whitelist.db", $client_addr)
if greylist("$client_addr-$f-$rcpt_addr", gltime)
if greylist_seconds_left = gltime
tempfail 450 4.7.0
"You are greylisted for %gltime seconds"
else
tempfail 450 4.7.0
"Still greylisted for " .
%greylist_seconds_left . " seconds"
fi
fi
fi
done
Mailfromd Manual:
For your reference, here is an alphabetical list of all reserved words:
Several keywords are context-dependent: mx is a keyword if it
appears before matches or fnmatches. Following strings
are keywords in on context:
The following keywords are preprocessor macros:
Any keyword beginning with a ‘m4_’ prefix is a reserved preprocessor symbol.
Mailfromd Manual:
This chapter describes library functions available in Mailfromd version 8.14. For the simplicity of explanation, we use the word ‘boolean’ to indicate variables of numeric type that are used as boolean values. For such variables, the term ‘False’ stands for the numeric 0, and ‘True’ for any non-zero value.
Mailfromd Manual:
Returns the value of Sendmail macro macro. If macro is
not defined, raises the e_macroundef exception.
Calling getmacro(name) is completely equivalent to
referencing ${name}, except that it allows to construct
macro names programmatically, e.g.:
if getmacro("auth_%var") = "foo"
…
fi
Return true if Sendmail macro name is defined.
Notice, that if your MTA supports macro name negotiation19, you will have to export macro names used by these two functions using ‘#pragma miltermacros’ construct. Consider this example:
func authcheck(string name)
do
string macname "auth_%name"
if macro_defined(macname)
if getmacro(macname)
…
fi
fi
done
#pragma miltermacros envfrom auth_authen
prog envfrom
do
authcheck("authen")
done
In this case, the parser cannot deduce that the envfrom handler
will attempt to reference the ‘auth_authen’ macro, therefore the
‘#pragma miltermacros’ is used to help it.
Mailfromd Manual:
sed functionThe sed function allows you to transform a string by replacing
parts of it that match a regular expression with another string. This
function is somewhat similar to the sed command line utility
(hence its name) and bears similarities to analogous functions in
other programming languages (e.g. sub in awk or the
s// operator in perl).
The expr argument is an s-expressions of the the form:
s/regexp/replacement/[flags]
where regexp is a regular expression, and replacement is a
replacement string for each part of the subject that matches
regexp. When sed is invoked, it attempts to match
subject against the regexp. If the match succeeds, the
portion of subject which was matched is replaced with
replacement. Depending on the value of flags
(see global replace), this process may continue until the entire
subject has been scanned.
The resulting output serves as input for next argument, if such is supplied. The process continues until all arguments have been applied.
The function returns the output of the last s-expression.
Both regexp and replacement are described in detail in The ‘s’ Command in GNU sed.
Supported flags are:
Apply the replacement to all matches to the regexp, not just the first.
Use case-insensitive matching. In the absence of this flag, the value
set by the recent #pragma regex icase is used (see icase).
regexp is an extended regular expression (see Extended regular expressions in GNU sed). In the absence of this flag, the value set by the
recent #pragma regex extended (if any) is used (see extended).
Only replace the numberth match of the regexp.
Note: the POSIX standard does not specify what should happen
when you mix the ‘g’ and number modifiers. Mailfromd
follows the GNU sed implementation in this regard, so
the interaction is defined to be: ignore matches before the
numberth, and then match and replace all matches from the
numberth on.
Any delimiter can be used in lieue of ‘/’, the only requirement being that it be used consistently throughout the expression. For example, the following two expressions are equivalent:
s/one/two/ s,one,two,
Changing delimiters is often useful when the regex contains
slashes. For instance, it is more convenient to write s,/,-, than
s/\//-/.
Here is an example of sed usage:
set email sed(input, 's/^<(.*)>$/\1/x')
It removes angle quotes from the value of the ‘input’ variable and assigns the result to ‘email’.
To apply several s-expressions to the same input, you can either give
them as multiple arguments to the sed function:
set email sed(input, 's/^<(.*)>$/\1/x', 's/(.+@)(.+)/\1\L\2\E/x')
or give them in a single argument separated with semicolons:
set email sed(input, 's/^<(.*)>$/\1/x;s/(.+@)(.+)/\1\L\2\E/x')
Both examples above remove optional angle quotes and convert the domain name part to lower case.
Regular expressions used in sed arguments are controlled by
the #pragma regex, as another expressions used throughout the
MFL source file. To avoid using the ‘x’ modifier in the above
example, one can write:
#pragma regex +extended set email sed(input, 's/^<(.*)>$/\1/', 's/(.+@)(.+)/\1\L\2\E/')
See regex, for details about that #pragma.
So far all examples used constant s-expressions. However, this is
not a requirement. If necessary, the expression can be stored in a
variable or even constructed on the fly before passing it as argument
to sed. For example, assume that you wish to remove the domain
part from the value, but only if that part matches one of predefined
domains. Let a regular expression that matches these domains be
stored in the variable domain_rx. Then this can be done as
follows:
set email sed(input, "s/(.+)(@%domain_rx)/\1/")
If the constructed regular expression uses variables whose value should be matched exactly, such variables must be quoted before being used as part of the regexp. Mailfromd provides a convenience function for this:
Quote the string str as a regular expression. This function selects the characters to be escaped using the currently selected regular expression flavor (see regex). At most two additional characters that must be escaped can be supplied in the delim optional parameter. For example, to quote the variable ‘x’ for use in double-quoted s-expression:
qr(x, '/"')
Mailfromd Manual:
Returns a copy of str with the characters from chars escaped, i.e. prefixed with a backslash. If chars is not specified, ‘\"’ is assumed.
escape('"a\tstr"ing') ⇒ '\"a\\tstr\"ing'
escape('new "value"', '\" ') ⇒ 'new\ \"value\"'
Performs the reverse to ‘escape’, i.e. removes any prefix backslash characters.
unescape('a \"quoted\" string') ⇒ 'a "quoted" string'
Returns the domain part of str, if it is a valid email address, otherwise returns str itself.
domainpart("gray") ⇒ "gray"
domainpart("gray@gnu.org.ua") ⇒ "gnu.org.ua"
Returns the index of the first occurrence of the string t in the string s, or -1 if t is not present.
index("string of rings", "ring") ⇒ 2
Optional argument start, if supplied, indicates the position in string where to start searching.
index("string of rings", "ring", 3) ⇒ 10
To find the last occurrence of a substring, use the function rindex (see rindex).
Converts str, which should be a valid time interval specification (see time interval specification), to seconds.
Returns the length of the string str in bytes.
length("string") ⇒ 6
Removes ‘<’ and ‘>’ surrounding str. If str is not enclosed by angle brackets or these are unbalanced, the argument is returned unchanged:
dequote("<root@gnu.org.ua>") ⇒ "root@gnu.org.ua"
dequote("root@gnu.org.ua") ⇒ "root@gnu.org.ua"
dequote("there>") ⇒ "there>"
Returns the local part of str if it is a valid email address, otherwise returns str unchanged.
localpart("gray") ⇒ "gray"
localpart("gray@gnu.org.ua") ⇒ "gray"
Replicate a string, i.e. return a string, consisting of s repeated n times:
replstr("12", 3) ⇒ "121212"
Returns the string composed of the characters from s in reversed order:
revstr("foobar") ⇒ "raboof"
Returns the index of the last occurrence of the string t in the string s, or -1 if t is not present.
rindex("string of rings", "ring") ⇒ 10
Optional argument start, if supplied, indicates the position in string where to start searching. E.g.:
rindex("string of rings", "ring", 10) ⇒ 2
See also String manipulation.
Returns the at most length-character substring of str starting at start. If length is omitted, the rest of str is used.
If length is greater than the actual length of the string, the
e_range exception is signalled.
substr("mailfrom", 4) ⇒ "from"
substr("mailfrom", 4, 2) ⇒ "fr"
Returns a substring of str between offsets start and
end, inclusive. Negative end means offset from the end of
the string. In other words, yo obtain a substring from start to the
end of the string, use substring(str, start, -1):
substring("mailfrom", 0, 3) ⇒ "mail"
substring("mailfrom", 2, 5) ⇒ "ilfr"
substring("mailfrom", 4, -1) ⇒ "from"
substring("mailfrom", 4, length("mailfrom") - 1) ⇒ "from"
substring("mailfrom", 4, -2) ⇒ "fro"
This function signals e_range exception if either start or
end are outside the string length.
Returns a copy of the string str, with all the upper-case characters translated to their corresponding lower-case counterparts. Non-alphabetic characters are left unchanged.
tolower("MAIL") ⇒ "mail"
Returns a copy of the string str, with all the lower-case characters translated to their corresponding upper-case counterparts. Non-alphabetic characters are left unchanged.
toupper("mail") ⇒ "MAIL"
Returns a copy of the input string str with any leading characters present in cset removed. If the latter is not given, white space is removed (spaces, tabs, newlines, carriage returns, and line feeds).
ltrim(" a string") ⇒ "a string"
ltrim("089", "0") ⇒ "89"
Note the last example. It shows how ltrim can be used to
convert decimal numbers in string representation that begins with
‘0’. Normally such strings will be treated as representing octal
numbers. If they are indeed decimal, use ltrim to strip off
the leading zeros, e.g.:
set dayofyear ltrim(strftime('%j', time()), "0")
Returns a copy of the input string str with any trailing characters present in cset removed. If the latter is not given, white space is removed (spaces, tabs, newlines, carriage returns, and line feeds).
Compares two strings as mailfromd version numbers. The
result is negative if b precedes a, zero if they refer to
the same version, and positive if b follows a:
vercmp("5.0", "5.1") ⇒ 1
vercmp("4.4", "4.3") ⇒ -1
vercmp("4.3.1", "4.3") ⇒ -1
vercmp("8.0", "8.0") ⇒ 0
Format code as a floating-point number with prec decimal digits:
sa_format_score(5000, 3) ⇒ "5.000"
This function is convenient for formatting SpamAssassin scores for use in message headers and textual reports. It is defined in module sa.mf.
See SpamAssassin, for examples of its use.
Format a SpamAssassin report text in order to include it in a RFC 822 header. This function selects the score listing from text, and prefixes each line with ‘* ’. Its result looks like:
* 0.2 NO_REAL_NAME From: does not include a real name * 0.1 HTML_MESSAGE BODY: HTML included in message
See SpamAssassin, for examples of its use.
Returns at most n last components of the domain name domain. If n is 0 the function returns domain.
This function is defined in the module strip_domain_part.mf (see Modules).
Examples:
require strip_domain_part
strip_domain_part("puszcza.gnu.org.ua", 2) ⇒ "org.ua"
strip_domain_part("puszcza.gnu.org.ua", 0) ⇒ "puszcza.gnu.org.ua"
Returns ‘true’ if str is a valid IPv4 address. This function is defined in the module is_ip.mf (see Modules).
For example:
require is_ip
is_ip("1.2.3.4") ⇒ 1
is_ip("1.2.3.x") ⇒ 0
is_ip("blah") ⇒ 0
is_ip("255.255.255.255") ⇒ 1
is_ip("0.0.0.0") ⇒ 1
Reverses octets in ip, which must be a valid string representation of an IPv4 address.
Example:
revip("127.0.0.1") ⇒ "1.0.0.127"
If email is a valid VERP-style email address for domain, this function returns the user name, corresponding to that email. Otherwise, it returns empty string.
verp_extract_user("gray=gnu.org.ua@tuhs.org", 'gnu\..*')
⇒ "gray"
Mailfromd Manual:
The function sprintf formats its argument according to
format (see below) and returns the resulting string. It takes
varying number of parameters, the only mandatory one being
format.
The format string is a simplified version of the format argument to
C printf-family functions.
The format string is composed of zero or more directives: ordinary characters (not ‘%’), which are copied unchanged to the output stream; and conversion specifications, each of which results in fetching zero or more subsequent arguments. Each conversion specification is introduced by the character ‘%’, and ends with a conversion specifier. In between there may be (in this order) zero or more flags, an optional minimum field width, and an optional precision.
Notice, that in practice that means that you should use single quotes with the format arguments, to protect conversion specifications from being recognized as variable references (see singe-vs-double).
No type conversion is done on arguments, so it is important that the
supplied arguments match their corresponding conversion specifiers.
By default, the arguments are used in the order given, where each
‘*’ and each conversion specifier asks for the next argument. If
insufficiently many arguments are given, sprintf raises
‘e_range’ exception. One can also specify explicitly which
argument is taken, at each place where an argument is required, by
writing ‘%m$’, instead of ‘%’ and ‘*m$’
instead of ‘*’, where the decimal integer m denotes the
position in the argument list of the desired argument, indexed
starting from 1. Thus,
sprintf('%*d', width, num);
and
sprintf('%2$*1$d', width, num);
are equivalent. The second style allows repeated references to the same argument.
The character ‘%’ is followed by zero or more of the following flags:
The value should be converted to an alternate form. For ‘o’ conversions, the first character of the output string is made zero (by prefixing a ‘0’ if it was not zero already). For ‘x’ and ‘X’ conversions, a non-zero result has the string ‘0x’ (or ‘0X’ for ‘X’ conversions) prepended to it. Other conversions are not affected by this flag.
The value should be zero padded. For ‘d’, ‘i’, ‘o’, ‘u’, ‘x’, and ‘X’ conversions, the converted value is padded on the left with zeros rather than blanks. If the ‘0’ and ‘-’ flags both appear, the ‘0’ flag is ignored. If a precision is given, the ‘0’ flag is ignored. Other conversions are not affected by this flag.
The converted value is to be left adjusted on the field boundary. (The default is right justification.) The converted value is padded on the right with blanks, rather than on the left with blanks or zeros. A ‘-’ overrides a ‘0’ if both are given.
A blank should be left before a positive number (or empty string) produced by a signed conversion.
A sign (‘+’ or ‘-’) always be placed before a number produced by a signed conversion. By default a sign is used only for negative numbers. A ‘+’ overrides a space if both are used.
An optional decimal digit string (with nonzero first digit) specifying a minimum field width. If the converted value has fewer characters than the field width, it will be padded with spaces on the left (or right, if the left-adjustment flag has been given). Instead of a decimal digit string one may write ‘*’ or ‘*m$’ (for some decimal integer m) to specify that the field width is given in the next argument, or in the m-th argument, respectively, which must be of numeric type. A negative field width is taken as a ‘-’ flag followed by a positive field width. In no case does a non-existent or small field width cause truncation of a field; if the result of a conversion is wider than the field width, the field is expanded to contain the conversion result.
An optional precision, in the form of a period (‘.’) followed by an optional decimal digit string. Instead of a decimal digit string one may write ‘*’ or ‘*m$’ (for some decimal integer m) to specify that the precision is given in the next argument, or in the m-th argument, respectively, which must be of numeric type. If the precision is given as just ‘.’, or the precision is negative, the precision is taken to be zero. This gives the minimum number of digits to appear for ‘d’, ‘i’, ‘o’, ‘u’, ‘x’, and ‘X’ conversions, or the maximum number of characters to be printed from a string for the ‘s’ conversion.
A character that specifies the type of conversion to be applied. The conversion specifiers and their meanings are:
The numeric argument is converted to signed decimal notation. The precision, if any, gives the minimum number of digits that must appear; if the converted value requires fewer digits, it is padded on the left with zeros. The default precision is ‘1’. When ‘0’ is printed with an explicit precision ‘0’, the output is empty.
The numeric argument is converted to unsigned octal (‘o’), unsigned decimal (‘u’), or unsigned hexadecimal (‘x’ and ‘X’) notation. The letters ‘abcdef’ are used for ‘x’ conversions; the letters ‘ABCDEF’ are used for ‘X’ conversions. The precision, if any, gives the minimum number of digits that must appear; if the converted value requires fewer digits, it is padded on the left with zeros. The default precision is ‘1’. When ‘0’ is printed with an explicit precision 0, the output is empty.
The string argument is written to the output. If a precision is specified, no more than the number specified of characters are written.
A ‘%’ is written. No argument is converted. The complete conversion specification is ‘%%’.
Mailfromd Manual:
These functions check whether all characters of str fall into a
certain character class according to the ‘C’ (‘POSIX’)
locale20. ‘True’ (1) is returned if they do, ‘false’ (0)
is returned otherwise. In the latter case, the global variable
ctype_mismatch is set to the index of the first character that
is outside of the character class (characters are indexed from 0).
Checks for alphanumeric characters:
isalnum("a123") ⇒ 1
isalnum("a.123") ⇒ 0 (ctype_mismatch = 1)
Checks for an alphabetic character:
isalnum("abc") ⇒ 1
isalnum("a123") ⇒ 0
Checks whether all characters in str are 7-bit ones, that fit into the ASCII character set.
isascii("abc") ⇒ 1
isascii("ab\0200") ⇒ 0
Checks if str contains only blank characters; that is, spaces or tabs.
Checks for control characters.
Checks for digits (0 through 9).
Checks for any printable characters except spaces.
Checks for lower-case characters.
Checks for printable characters including space.
Checks for any printable characters which are not a spaces or alphanumeric characters.
Checks for white-space characters, i.e.: space, form-feed (‘\f’), newline (‘\n’), carriage return (‘\r’), horizontal tab (‘\t’), and vertical tab (‘\v’).
Checks for uppercase letters.
Checks for hexadecimal digits, i.e. one of ‘0’, ‘1’, ‘2’, ‘3’, ‘4’, ‘5’, ‘6’, ‘7’, ‘8’, ‘9’, ‘a’, ‘b’, ‘c’, ‘d’, ‘e’, ‘f’, ‘A’, ‘B’, ‘C’, ‘D’, ‘E’, ‘F’.
Mailfromd Manual:
MFL provides a set of functions for writing to disk files,
pipes or sockets and reading from them. The idea behind them is the
same as in most other programming languages: first you open the
resource with a call to open which returns a descriptor
i.e. an integer number uniquely identifying the resource. Then you
can write or read from it using this descriptor. Finally, when the
resource is no longer needed, you can close it with a call to
close.
The number of available resource descriptors is limited. The
default limit is 1024. You can tailor it to your needs
using the max-streams runtime configuration statement.
See max-streams, for a detailed description.
By default, all I/O operations are unbuffered. This can be changed by setting the following global variables:
Sets the default buffering type. Allowed values are (symbolic names are defined in status.mf module):
0BUFFER_NONENo buffering. This is the default.
1BUFFER_FULLFull buffering. Size of the buffer is set by the
io_buffer_size global variable (see below).
2BUFFER_LINELine buffering. When reading, it is pretty much the same as
BUFFER_FULL. When writing, the data are accumulated in buffer
and actually sent to the underlying transport stream when the newline
character is seen.
The initial size of the buffer is set by the io_buffer_size
variable. It will grow as needed during the I/O.
Set the buffer size if io_buffering is set to
BUFFER_FULL or BUFFER_LINE. By default, this variable
is set to the size of the system page.
The name argument specifies the name of a resource to open and the access rights you need to have on it. The function returns a descriptor of the opened stream, which can subsequently be used as an argument to other I/O operations.
Buffering mode for the opened stream is defined by the
io_buffering and io_buffer_size global variables. It
can be changed using the setbuf function (see setbuf).
First symbols of name determine the type of the resource to be opened and the access mode:
The rest of name is a name of a file. Open the file for read-write access. If the file exists, truncate it to zero length, otherwise create the file.
The rest of name is a name of a file. Open the file for appending (writing at end of file). The file is created if it does not exist.
Treat the rest of name as the command name and its arguments. Run this command and open its standard input for writing. The standard error is closed before launching the program. This can be altered by using the following versions of this construct:
Standard error is redirected to /dev/null.
Execute command with its standard error redirected to the file name. If the file exists, it will be truncated.
Standard error of the command is appended to the file name. If file does not exist, it will be created.
The ‘|2>null:’ construct described above is a shortcut for
|2>>file:/dev/null command
Standard error is redirected to the given syslog facility and, optionally, priority. If the latter is omitted, ‘LOG_ERR’ is assumed.
Valid values for facility are: ‘user’, ‘daemon’, ‘auth’, ‘authpriv’, ‘mail’, and ‘local0’ through ‘local7’. Valid values for priority are: ‘emerg’, ‘alert’, ‘crit’, ‘err’, ‘warning’, ‘notice’, ‘info’, ‘debug’. Both facility and priority may be given in upper, lower or mixed cases.
Notice, that no whitespace characters are allowed between ‘|’ and ‘2>’.
Treat the rest of name as the command name and its arguments. Run this command with its stdin closed and stdout open for reading.
The standard error is treated as described above (see ‘|’).
Treat the rest of name as the command name and its arguments.
Run this command and set up for two-way communication with it, i.e
writes to the descriptor returned by open will send data to the
program’s standard input, reads from the descriptor will get data from
the program’s standard output.
The standard error is treated as described above (see ‘|’). For example, the following redirects it to syslog ‘mail.debug’:
|&2>syslog:mail.debug command
Treat the rest of name as the URL of a socket to connect to. Valid URL forms are described in milter port specification.
If none of these prefixes is used, name is treated as a name
of an existing file and open will attempt to open this file for
reading.
The open function will signal exception e_failure if it
is unable to open the resource or get the required access to it.
Runs the supplied command cmd. The syntax of the cmd is
the same as for the name argument to open (see above),
which begins with ‘|’, excepting that the ‘|’ sign is
optional. That is:
spawn("/bin/cat")
has exactly the same effect as
open("|/bin/cat")
Optional arguments specify file stream descriptors to be used for the
program standard input, output and error streams, correspondingly.
If supplied, these should be the values returned by a previous call to
open or tempfile. The value ‘-1’ means no
redirection.
Buffering mode for the opened stream is defined by the
io_buffering and io_buffer_size global variables. It
can be changed using the setbuf function (see setbuf).
The example below starts the awk program with a simple
expression as its argument and redirects the content of the
file /etc/passwd to its standard input. The returned
stream descriptor is bound to the command’s standard output
(see the description of ‘|<’ prefix above). The standard
error is closed:
number fd spawn("<awk -F: '{print $1}'", open("/etc/passwd"))
The argument rd is a resource descriptor returned by a
previous call to open. The function close closes the
resource and deallocates any memory associated with it.
close will signal e_range exception if rd lies
outside of allowed range of resource descriptors. See max-streams.
Notice that you are not required to close resources opened by open.
Any unclosed resource will be closed automatically upon the
termination of the filtering program.
This function causes all or part of a full-duplex connection to be
closed. The rd must be either a socket descriptor (returned by
open(@...)) or a two-way pipe socket descriptor (returned by
open(|&...)), otherwise the call to shutdown is
completely equivalent to close.
The how argument identifies which part of the connection to
shut down:
Read connection. All further receptions will be disallowed.
Write connection. All further transmissions will be disallowed.
Shut down both read and write parts.
Creates a nameless temporary file and returns its descriptor. Optional tmpdir supplies the directory where to create the file, instead of the default /tmp.
Rewinds the stream identified by rd to its beginning.
Copies all data from the stream src to dst. Returns number of bytes copied.
The following functions provide basic read/write capabilities.
Writes the string str to the resource descriptor rd. If the size argument is given, writes this number of bytes.
This function always attempts to write the requested amount of
data. It will signal e_range exception if rd lies
outside of allowed range of resource descriptors, e_io
exception if an I/O error occurs, and e_eof exception
if it wrote 0 bytes (e.g. because the underlying device is full).
Write the body segment of length size from pointer bp to
the stream rd. This function can be used only in prog
body (see body handler). Its second and third arguments
correspond exactly to the parameters of the body handler, so
the following construct writes the message body to the resource
fd, which should have been open prior to invoking the
body handler:
prog body do write_body(fd, $1, $2) done
Read and return at most n bytes from the resource descriptor rd.
If there are less than n bytes in the stream, the remaining
bytes will be returned. Use length() to obtain the actual size
of the returned data. If there are no bytes left, the e_eof
exception will be signalled.
The function may signal the following exceptions:
rd lies outside of allowed range of resource descriptors.
End of file encountered.
An I/O error occurred.
Read and return the next string terminated by delim from the resource descriptor rd.
The terminating delim string will be removed from the return value.
When using this function, it is highly recommended to enable full
buffering for fd, either by setting io_buffering before
open (see io_buffering) or by calling setbuf
after it (see setbuf). See getline, for an example.
This function may signal the following exceptions:
rd lies outside of allowed range of resource descriptors.
End of file encountered.
An I/O error occurred.
Read and return the next line from the resource
descriptor rd. A line is any sequence of characters terminated
with the default line delimiter. The default delimiter is
a property of rd, i.e. different descriptors can have different
line delimiters. The default value is ‘\n’ (ASCII 10), and can
be changed using the fd_set_delimiter function (see below).
When using this function, it is highly recommended to enable full
buffering for fd, either by setting io_buffering before
open (see io_buffering) or by calling setbuf
after it (see setbuf), e.g.:
set fd open(input) setbuf(fd, BUFFER_FULL) set line getline(fd) ...
This function may signal the following exceptions:
rd lies outside of allowed range of resource descriptors.
End of file encountered.
An I/O error occurred.
Set new line delimiter for the descriptor fd, which must be in opened state.
Default delimiter is a newline character (ASCII 10). The following example shows how to change it to CRLF sequence:
fd_set_delimiter(fd, "\r\n")
Returns the line delimiter string for fd.
The following example shows how mailfromd I/O functions can
be used to automatically add IP addresses to an RBL zone:
set nsupdate_cmd
"/usr/bin/nsupdate -k /etc/bind/Kmail.+157+14657.private"
func block_address(string addr)
do
number fd
string domain
set fd open "|%nsupdate_cmd"
set domain revip(addr) . ".rbl.myzone.come"
write(fd, "prereq nxrrset %domain A\n"
"update add %domain 86400 A %addr\n\n"
done
The function revip is defined in revip.
Changes the buffering mode of fd according to the remaining two
arguments. The type specifies buffering type
(see io_buffering), and size supplies the buffer size for
buffering types BUFFER_FULL and BUFFER_LINE. If
size is omitted, it defaults to io_buffer_size
(see io_buffer_size). Omitted type defaults to
io_buffering (see io_buffering).
Returns the type of buffering currently in effect for the descriptor fd. See io_buffering, for a list of possible return values.
If this function returns BUFFER_FULL or BUFFER_LINE, you
can use getbufsize to get the associated buffer size.
Returns the buffer size for the descriptor fd.
Mailfromd Manual:
This section describes functions that transform data using
Mailutils filter pipes. Filter pipe is a string defining data
flow between several filters. Each filter takes input,
transforms it according to certain rules and produces the transformed
data on its output. As in shell, multiple filters are connected
using pipe characters (‘|’). For example, the crlf filter
inserts a carriage return character before each newline character. A
filter doing that kind of transformation is defined as:
"crlf"
Another filter, base64, converts its input to a BASE64 encoded
string. To transform each newline into carriage return + newline pair
and encode the resulting stream in BASE64, one would write:
"crlf | base64"
Some filters take one or more arguments. These are specified as
a comma-delimited list in parentheses after the filter name. For
example, the linelen filter limits the length of each output
line to the given number of octets. The following filter pipe will
limit the length of base64 lines in the filter above to 62 octets:
"crlf | base64 | linelen(62)"
Many filters operate in two modes: encode and decode. By
default all MFL functions apply filters in encode mode. The desired
mode can be stated explicitly in the filter string by using
encode() and decode() functions. They take a filter
pipe line as their argument. For example, the following will decode
the stream produced by the example filter above:
"decode(base64 | crlf)"
See Filters, for a discussion of available filters and their arguments.
Transforms the string input using filters in filter_pipe and returns the result. Example:
set input "test\ninput\n" filter_string(input, "crlf|base64") ⇒ "dGVzdA0KaW5wdXQNCg=="
Given two I/O descriptors, reads data from src_fd, transforms it using filter_pipe and writes the result to descriptor dst_fd.
Both descriptors must be obtained using functions described in I/O functions.
Mailfromd Manual:
A filter pipe is a string consisting of filter invocations
delimited by pipe characters (‘|’). Each invocation
is a filter name optionally followed by a comma-separated list of
parameters. Most filters can operate in two modes: encode and
decode. Unless specified otherwise, filters are invoked in
encode mode. To change the mode, the encode and decode
meta-filters are provided. Argments to these filters are filter pipes
that will be executed in the corresponding mode.
The following Mailutils filters are available:
In encode mode, converts its input into 7-bit ASCII, by clearing the 8th bit on each processed byte.
In decode mode, it operates exactly as the 8bit filter, i.e. copies its input to the output verbatim.
The filter takes no arguments.
Copies its input to output verbatim.
Encodes or decodes the input using the base64 encoding.
The only difference between BASE64 and B is that, in
encode mode, the former limits each ouput line length to 76 octets,
whereas the latter produces a contiguous stream of base64 data.
In decode mode, both filters operate exactly the same way.
A convenience interface to the iconv filter, available for use
only in the message_body_to_stream function. It decodes the
part of a MIME message from its original character set, which is
determined from the value of the Content-Type header, to the
destination character set cset. Optional fallback
parameter specifies the representation fallback to be used for octets
that cannot be converted between the charater sets. Its use is
described in See iconv.
This filter is normally takes its input from the mimedecode
filter, as in:
message_body_to_stream(fd, msg, 'mimedecode|charset(utf-8)')
See mimedecode, for a detailed discussion.
Converts line separators from LF (ASCII 10) to CRLF (ASCII 13 10) and vice-versa.
In decode mode, translates each CRLF to LF. Takes no arguments.
In encode mode, translates each LF to CRLF. If an optional argument ‘-n’ is given, produces a normalized output, by preserving each input CRLF sequence untouched (otherwise such sequences will be are translated to CR CR LF).
In encode mode, replaces each LF (‘\n’ or ASCII 10) character with CRLF (‘\r\n’, ASCII 13 10), and byte-stuffs the output by producing an additional ‘.’ in front of any ‘.’ appearing at the beginning of a line in input. Upon end of input, it outputs additional ‘.\r\n’, if the last output character was ‘\n’, or ‘\r\n.\r\n’ otherwise.
If supplied the ‘-n’ argument, it preserves each CRLF input
sequence untranslated (see the CRLF above).
In decode mode, the reverse is performed: each CRLF is replaced with a single LF byte, and additional dots are removed from beginning of lines. A single dot on a line by itself marks the end of the stream and causes the filter to return EOF.
In encode mode, byte-stuffs the input by outputting an additional dot (‘.’) in front of any dot appearing at the beginning of a line. Upon encountering end of input, it outputs additional ‘.\n’.
In decode mode, the reverse is performed: additional dots are removed from beginning of lines. A single dot on a line by itself (i.e. the sequence ‘\n.\n’) marks the end of the stream and causes the filter to return EOF.
This filter doesn’t take arguments.
Performs a traditional UNIX processing of lines starting with a ‘From’ followed by a space character.
In encode mode, each ‘From ’ at the beginning of a line is replaced by ‘>From ’.
In decode mode, the reverse operation is performed: initial greater-then sign (‘>’) is removed from any line starting with ‘>From ’.
The filter takes no arguments.
MBOXRD-compatible processing of envelope lines.
In encode mode, each ‘From ’ optionally preceded by any number of contiguous ‘>’ characters and appearing at the beginning of a line is prefixed by another ‘>’ character on output.
In decode mode, the reverse operation is performed: initial greater-then sign (‘>’) is removed from any line starting with one or more ‘>’ characters followed by ‘From ’.
This filter treats its input as a RFC-2822 email message. It extracts its header part (i.e. everything up to the first empty line) and copies it to the output. The body of the message is ignored.
The filter operates only in decode mode and takes no arguments.
Converts input from character set src to dst. The filter works the same way in both decode and encode modes.
It takes two mandatory arguments: the names of the input (src) and output (dst) charset. Optional third argument specifies what to do when an illegal character sequence is encountered in the input stream. Its possible values are:
Raise a e_ilseq exception.
Copy the offending octet to the output verbatim and continue conversion from the next octet.
Print the offending octet to the output using the C octal conversion and continue conversion from the next octet.
The default is copy-octal.
The following example creates a iconv filter for converting from
iso-8859-2 to utf-8, raising the e_ilseq
exception on the first conversion error:
iconv(iso-8859-2, utf-8, none)
In decode mode, the filter removes from the input all lines beginning with a given inline comment sequence str. The default comment sequence is ‘;’ (a semicolon).
The following options modify the default behavior:
Emit line number information after each contiguous sequence of removed lines. The argument str supplies an information starter – a sequence of characters which is output before the actual line number.
Remove empty lines, i.e. the lines that contain only whitespace characters.
Squeeze whitespace. Each sequence of two or more whitespace characters encountered on input is replaced by a single space character on output.
A whitespace-must-follow mode. A comment sequence is recognized only if followed by a whitespace character. The character itself is retained on output.
In encode mode the inline-comment filter adds a comment-starter
sequence at the beginning of each line. The default comment-starter
is ‘;’ and can be changed by specifying the desired comment
starter as the first argument.
The only option supported in this mode is -S, which enables the whitespace-must-follow mode, in which a single space character (ASCII 20) is output after each comment sequence.
Implements a familiar UNIX line-continuation facility. The filter removes from itsinput stream any newline character immediately preceded by a backslash. This filter operates only in decode mode.
If given the arguments (‘-i’, str), enables the line number information facility. This facility emits current input line number (prefixed with str) after each contiguous sequence of one or more removed newline characters. It is useful for implementing parsers which are normally supposed to identify eventual erroneous lines with their input line numbers.
Limits the length of each output line to a certain number of octets. It operates in encode mode only and requires a single parameter: the desired output length in octets. This filter makes no attempt to analyze the lexical structure of the input: the newline caracters are inserted when the length of the output line reaches a predefined maximum. Any newline characters present in the input are taken into account when computing the input line length.
This is a domain-specific filter available for use only with the
message_body_to_stream function. It decodes the part of
a MIME message from whatever encoding that was used to store it
in the message to a stream of bytes. See mimedecode.
Encodes or decodes the input using the quoted-printable encoding.
In encode mode, the xml filter converts input stream (which must
contain valid UTF-8 characters) into a form suitable for inclusion into
a XML or HTML document, i.e. it replaces ‘<’, ‘>’, and
‘&’ with ‘<’, ‘>’, and ‘&’,
correspondingly, and replaces invalid characters with their numeric
character reference representation.
In decode mode, a reverse operation is performed.
The filter does not take arguments.
Mailfromd Manual:
Parses email and returns a bitmap, consisting of zero or more of the following flags:
email has more than one email address.
email has comment parts.
email has personal part.
email has local part.
email has domain part.
email has route part.
These constants are declared in the email.mf module. The
function email_map returns 0 if its argument is not a valid
email address.
Returns ‘True’ (1) if email is a valid email address, consisting of local and domain parts only. E.g.:
email_valid("gray@gnu.org") ⇒ 1
email_valid("gray") ⇒ 0
email_valid('"Sergey Poznyakoff <gray@gnu.org>') ⇒ 0
This function is defined in email.mf (see Modules).
Mailfromd Manual:
Envelope modification functions set sender and add or delete recipient addresses from the message envelope. This allows MFL scripts to redirect messages to another addresses.
Sets envelope sender address to email, which must be a valid email address. Optional args supply arguments to ESMTP ‘MAIL FROM’ command.
Add the e-mail address to the envelope.
Remove address from the envelope.
The following example code uses these functions to implement a simple alias-like capability:
prog envrcpt
do
string alias dbget(aliasdb, $1, "NULL", 1)
if alias != "NULL"
rcpt_delete($1)
rcpt_add(alias)
fi
done
Mailfromd Manual:
There are two ways to modify message headers in a MFL script. First is to use header actions, described in Actions, and the second way is to use message modification functions. Compared with the actions, the functions offer a series of advantages. For example, using functions you can construct the name of the header to operate upon (e.g. by concatenating several arguments), something which is impossible when using actions. Moreover, apart from three basic operations (add, modify and remove), as supported by header actions, header functions allow to insert a new header into a particular place.
Adds a header ‘name: value’ to the message.
In contrast to the add action, this function allows to construct
the header name using arbitrary MFL expressions.
This syntax is preserved for backward compatibility. It is equivalent
to header_insert, which see.
This function inserts a header ‘name: ‘value’’ at
idxth header position in the internal list of headers maintained
by the MTA. That list contains headers added to the message either by
the filter or by the MTA itself, but not the headers included in the
message itself. Some of the headers in this list are conditional,
e.g. the ones added by the ‘H?cond?’ directive in
sendmail.cf. MTA evaluates them after all header modifications
have been done and removes those of headers for which they yield false.
This means that the position at which the header added by
header_insert will appear in the final message will differ from
idx.
Delete header name from the envelope. If index is given, delete indexth instance of the header name.
Notice the differences between this function and the delete
action:
delete
requires it to be a literal string.
Replace the value of the header name with value. If index is given, replace indexth instance of header name.
Notice the differences between this function and the replace
action:
replace
requires it to be a literal string.
Defined in the module header_rename.mf.
Available only in the ‘eom’ handler.
Renames the idxth instance of header name to newname. If idx is not given, assumes 1.
If the specified header or the idx instance of it is not present in the current message, the function silently returns. All other errors cause run-time exception.
The position of the renamed header in the header list is not preserved.
The example below renames ‘Subject’ header to ‘X-Old-Subject’:
require 'header_rename'
prog eom
do
header_rename("Subject", "X-Old-Subject")
done
Defined in the module header_rename.mf.
Available only in the ‘eom’ handler.
Renames all headers named name by prefixing them with prefix. If prefix is not supplied, removes all such headers.
All renamed headers will be placed in a continuous block in the header list. The absolute position in the header list will change. Relative ordering of renamed headers will be preserved.
Defined in the module header_rename.mf.
Available only in the ‘eom’ handler.
Renames all headers with names matching pattern (in the sense of
fnmatch, see fnmatches) by prefixing
them with prefix.
All renamed headers will be placed in a continuous block in the header list. The absolute position in the header list will change. Relative ordering of renamed headers will be preserved.
If called with one argument, removes all headers matching pattern.
For example, to prefix all headers beginning with ‘X-Spamd-’ with an additional ‘X-’:
require 'header_rename'
prog eom
do
header_prefix_pattern("X-Spamd-*", "X-")
done
Mailfromd Manual:
Body modification is an experimental feature of MFL. The version 8.14 provides only one function for that purpose.
Replace the body of the message with text. Notice, that text must not contain RFC 822 headers. See the previous section if you want to manipulate message headers.
Example:
replbody("Body of this message has been removed by the mail filter.")
No restrictions are imposed on the format of text.
Replaces the body of the message with the content of the stream fd. Use this function if the body is very big, or if it is returned by an external program.
Notice that this function starts reading from the current position in
fd. Use rewind if you wish to read from the beginning of
the stream.
The example below shows how to preprocess the body of the message using external program /usr/bin/mailproc, which is supposed to read the body from its standard input and write the processed text to its standard output:
number fd # Temporary file descriptor
prog data
do
# Open the temporary file
set fd tempfile()
done
prog body
do
# Write the body to it.
write_body(fd, $1, $2)
done
prog eom
do
# Use the resulting stream as the stdin to the mailproc
# command and read the new body from its standard output.
rewind(fd)
replbody_fd(spawn("</usr/bin/mailproc", fd))
done
Mailfromd Manual:
Message modification functions described in the previous subsections do not take effect immediately, in the moment they are called. Instead they store the requested changes in the internal message modification queue. These changes are applied at the end of processing, before ‘eom’ stage finishes (see Figure 3.1).
One important consequence of this way of operation is that calling
any MTA action (see Actions), causes all prior
modifications to the message to be ignored. That is because after
receiving the action command, MTA will not call filter
for that message any more. In particular, the ‘eom’ handler will
not be called, and the message modification queue will not be flushed.
While it is logical for such actions as reject or
tempfail, it may be quite confusing for accept.
Consider, for example, the following code:
prog envfrom
do
if $1 == ""
header_add("X-Filter", "foo")
accept
fi
done
Obviously, the intention was to add a ‘X-Filter’ header and accept the message if it was sent from the null address. What happens in reality, however, is a bit different: the message is accepted, but no header is added to it. If you need to accept the message and retain any modifications you have done to it, you need to use an auxiliary variable, e.g.:
number accepted 0
prog envfrom
do
if $1 == ""
header_add("X-Filter", "foo")
set accepted 1
fi
done
Then, test this variable for non-zero value at the beginning of each subsequent handler, e.g.:
prog data
do
if accepted
continue
fi
...
done
To help you trace such problematic usages of accept,
mailfromd emits the following warning:
RUNTIME WARNING near /etc/mailfromd.mf:36: `accept' causes previous message modification commands to be ignored; call mmq_purge() prior to `accept', to suppress this warning
If it is OK to lose all modifications, call mmq_purge, as
suggested in this message.
Remove all modification requests from the queue. This function undoes
the effect of any of the following functions, if they had been called
previously: rcpt_add, rcpt_delete, header_add,
header_insert, header_delete, header_replace,
replbody, quarantine.
Mailfromd Manual:
Encode text in accordance with RFC 2047. Optional arguments:
Encoding to use. Valid values are ‘quoted-printable’, or ‘Q’ (the default) and ‘base64’, or ‘B’.
Character set. By default ‘UTF-8’.
If the function is unable to encode the string, it raises the
exception e_failure.
For example:
set string "Keld Jørn Simonsen <keld@dkuug.dk>" message_header_encode(string, "ISO-8859-1") ⇒ "=?ISO-8859-1?Q?Keld_J=F8rn_Simonsen?= <keld@dkuug.dk>"
text must be a header value encoded in accordance with RFC
2047. The function returns the decoded string. If the decoding fails,
it raises e_failure exception. The optional argument
charset specifies the character set to use (default –
‘UTF-8’).
set string "=?ISO-8859-1?Q?Keld_J=F8rn_Simonsen?= <keld@dkuug.dk>" message_header_decode(string) ⇒ "Keld Jørn Simonsen <keld@dkuug.dk>"
If text is a “folded” multi-line RFC 2822 header value, unfold it. If text is a single-line string, return its unchanged copy.
For example, suppose that the message being processed contained the following header:
List-Id: Sent bugreports to <some-address@some.net>
Then, applying unfold to its value21 will produce:
Sent bugreports to <some-address@some.net>
Mailfromd Manual:
Converts first count bytes from the memory location pointed to by text into a regular string.
This function is intended to convert the $1 argument passed to
a body handler to a regular MFL string. For more
information about its use, see body handler.
Returns ‘True’ if first count bytes of the string pointed to by text contain ASCII NUL characters.
Example:
prog body
do
if body_has_nulls($1, $2)
reject
fi
done
Mailfromd Manual:
The following function is available only in the ‘eom’ handler:
Notify the MTA that the filter is still processing the message. This causes MTA to restart its timeouts and allows additional amount of time for execution of ‘eom’.
Use this function if your ‘eom’ handler needs additional time for processing the message (e.g. for scanning a very big MIME message). You may call it several times, if the need be, although such usage is not recommended.
Mailfromd Manual:
This function can be used in eom handlers only. It returns a
message descriptor referring to the current message. See Message functions, for a description of functions for accessing messages.
The functions below access the headers from the current message. They
are available in the following handlers: eoh, body, eom.
Return number of headers in the current message. If name is specified, return number of headers that have this name.
current_header_count() ⇒ 6
current_header_count("Subject") ⇒ 1
Return the name of the nth header. The index n is 1-based.
Return the value of the nth header. The index n is 1-based.
Return the value of the named header, e.g.:
set s current_header("Subject")
Optional second argument specifies the header instance, if there are more than 1 header of the same name, e.g.:
set s current_header("Received", 2)
Header indices are 1-based.
All current_header function raise the e_not_found exception if the
requested header was not found.
Mailfromd Manual:
A set of functions is provided for accessing mailboxes and messages within them. In this subsection we describe the functions for accessing mailboxes.
A mailbox is opened using mailbox_open function:
Open a mailbox identified by url. Return a mailbox descriptor: a unique numeric identifier that can subsequently be used to access this mailbox.
The optional mode argument specifies the access mode for the mailbox. Its valid values are:
| Value | Meaning |
|---|---|
| r | Open mailbox for reading. This is the default. |
| w | Open mailbox for writing. If the mailbox does not exist, it is created. |
| rw | Open mailbox for reading and writing. If the mailbox does not exist, it is created. |
| wr | Same as ‘rw’. |
| w+ | Open mailbox for reading and writing. If the mailbox does not exist, it is created. |
| a | Open mailbox for appending messages to it. If the mailbox does not exist, an exception is signalled. |
| a+ | Open mailbox for appending messages to it. If the mailbox does not exist, it is created. |
The optional perms argument specifies the permissions to use in case a new file (or files) is created. It is a comma-separated list of:
[go](+|=)[wr]+
The initial letter controls which users’ access is to be set: users in the file’s group (‘g’) or other users not in the file’s group (‘o’). The following character controls whether the permissions are added to the default ones (‘+’) or applied instead of them (‘=’). The remaining letters specify the permissions: ‘r’ for read access and ‘w’ for write access. For example:
g=rw,o+r
The number of mailbox descriptors available for simultaneous opening
is 64. This value can be changed using the
max-open-mailboxes runtime configuration statement
(see max-open-mailboxes).
Return the number of messages in mailbox. The argument nmbx is
a valid mailbox descriptor as returned by a previous call to
mailbox_open.
Retrieve nth message from the mailbox identified by descriptor mbx. On success, the function returns a message descriptor, an integer number that can subsequently be used to access that message (see Message functions). On error, an exception is raised.
Messages in a mailbox are numbered starting from 1.
Close a mailbox previously opened by mailbox_open.
Append message nmsg to mailbox nmbx. The message
descriptor nsmg must be obtained from a previous call to
mailbox_get_message or current_message
(see current_message).
Mailfromd Manual:
The functions described below retrieve information from RFC822
messages. The message to operate upon is identified by its
descriptor, an integer number returned by the previous call to
mailbox_get_message (see mailbox_get_message) or current_message
(see current_message) function. The maximum number of message
descriptors is limited by 1024. You can change this limit
using the max-open-messages runtime configuration statement
(see max-open-messages).
Return the size of the message nmsg, in bytes. Notice,
that if nmsg refers to current message
(see current_message), the returned value is less than the size
seen by the MTA, because mailfromd recodes
CR-LF sequences to LF, i.e. removes carriage
returns (ASCII 13) occurring before line feeds
(ASCII 10. To obtain actual message length as seen by the
MTA, add the number of lines in the message:
set actual_length message_size(nmsg) + message_lines(nmsg)
Returns true if the body of message nmsg has zero size or
contains only whitespace characters. If the
‘Content-Transfer-Encoding’ header is present, it is used to
decode body before processing.
Close the message identified by descriptor nmsg.
Return total number of lines in message nmsg. The following relation holds true:
message_lines(x) = message_body_lines(x)
+ message_header_lines(x) + 1
Read and return next line from the message nmsg. If
there are no more lines to read, raise the eof exception.
Use message_rewind to rewind the message stream and read its
contents again.
Rewind the stream associated with message referred to by descriptor nmsg.
Converts contents of the stream identified by fd to a mail message. Returns identifier of the created message.
Optional filter_chain supplies the name of a Mailutils filter chain, through which the data will be passed before converting. See http://mailutils.org/wiki/Filter_chain, for a description of filter chains.
Copies message nsmg to stream descriptor fd. The
descriptor must be obtained by a previous call to open.
Optional filter_chain supplies the name of a Mailutils filter chain, through which the data will be passed before writing them to fd. See http://mailutils.org/wiki/Filter_chain, for a description of filter chains.
Mailfromd Manual:
Return the size, in bytes of the headers of message nmsg. See the
note to the message_size, above.
Return number of lines occupied by headers in message nmsg.
Return number of headers in message nmsg.
If name is supplied, count only headers with that name.
Return value of header name from the message nmsg. If the message contains several headers with the same name, optional parameter idx may be used to select one of them. Headers are numbered from ‘1’.
If no matching header is not found, the not_found exception is
raised. If another error occurs, the failure exception is
raised.
The returned string is a verbatim copy of the message contents (except
for eventual CR-LF -> LF translation, see above).
You might need to apply the unfold function to it (see unfold).
Returns the name of the nth header in message nmsg. If
there is no such header, e_range exception is raised.
Returns the value of the nth header in message nmsg. If
there is no such header, e_range exception is raised.
Return true if message nmsg contains header with the
given name. If there are several headers with the same name,
optional parameter idx may be used to select one of them.
Mailfromd Manual:
Return the size, in bytes, of the body of message nmsg. See the
note to the message_size, above.
Return number of lines in the body of message referred to by descriptor nmsg.
Rewind the stream associated with the body of message referred to by descriptor nmsg.
A call to message_body_read_line (see below) after calling this
function will return the first line from the message body.
Read and return next line from the body of the message nmsg. If
there are no more lines to read, raise the eof exception.
Use message_body_rewind (see above) to rewind the body stream
and read its contents again.
Copies the body of the message nsmg to stream descriptor
fd. The descriptor must be obtained by a previous call to
open.
Optional filter_pipe supplies a sequence of Mailutils filters, through which the data will be passed before writing them to fd. See Filtering functions, for a discussion of filter pipe syntax.
In addition to filters described in See Filters, two special
filters are provided for use with this function: mimedecode and
charset. The mimedecode filter instructs the function
to decode the message body by reverting the encoding specified by its
Content-Transfer-Encoding header. It is normally used as the
very first filter in chain. The charset filter recodes the
message body from it original character set to the character set
specified as its argument.
See mimedecode, for a detailed discussion of this feature.
Mailfromd Manual:
Return true if message nmsg is a multipart
(MIME) message.
Return number of parts in message nmsg, if it is a multipart (MIME) message. If it is not, return ‘1’.
Use message_is_multipart to check whether the message is a
multipart one.
Extract nth part from the multipart message nmsg. Numeration of parts begins from ‘1’. Return message descriptor referring to the extracted part. Message parts are regarded as messages, so any message functions can be applied to them.
Returns content type for the message nmsg. The returned string is composed of content type and subtype, delimited by slash.
If nmsg is not a multipart message, the function returns ‘text/plain’.
Several functions are provided for decoding multi-part messages. Such
decoding is governed by Content-Transfer-Encoding and
Content-Type headers of the message. The
Content-Transfer-Encoding header defines the method used to
encode the message. The value of Content-Type header is used
to determine the character set the body is written in.
Basic MIME decoding facilities are provided by the built-in function
message_body_to_stream, described in the previous subsection.
To instruct it to decode the content, pass it the filter_chain
argument beginning with the word mimedecode. The usual
sequence is:
set fd open("> outfile")
message_body_to_stream(fd, msg, "mimedecode")
To ensure that the produced stream is represented in a specific
character set, use the charset special filter. Its argument is
the name of the character set to recode the text to:
set fd open("> outfile")
message_body_to_stream(fd, msg, "mimedecode|charset(utf-8)")
The charset filter takes also an optional second argument – a
fallback method, specifying what to do when an octet sequence is
encountered that cannot be represented in the requested character set.
Possible values for this argument are:
Stop further conversion and signal the e_ilseq exception.
Copy the offending character to the output verbatim.
Represent the offending character as a C octal sequence (‘\nnn’, where n is an octal digit). This is the default.
To decode a particular part of the message, first extract it using the
message_get_part function. Recall that message parts are
messages as well, and as such can be passed to
message_body_to_stream. For example, the following code
fragment extracts all top-level parts of a multi-part message to files
named ‘part.N’:
if message_is_multipart(msg)
set n message_count_parts(msg)
loop for set i 1, while i <= n, set i i + 1
do
set fd open("> part.%i")
message_body_to_stream(fd, message_get_part(msg, i), "mimedecode")
close(fd)
done
fi
The mime.mf module provides additional functions for decoding multi-part messages:
Decodes the body of the message (or message part) nmsg, optionally converting it to the given charset. The fallback argument specifies what to do if a byte sequence cannot be converted to the specified character set. See iconv fallback, for a detailed discussion.
The function returns a descriptor of the I/O stream that contains the decoded material. See I/O functions for a discussion of functions available for reading from it.
Decodes the body of the given part of a MIME message nmsg. The
argument part is a 1-based index of the part in the message.
Optional arguments charset and fallback have the same
meaning as in message_body_decode (see above).
Returns a descriptor of the I/O stream that contains the decoded material.
This function is equivalent to:
message_body_decode(message_get_part(nmsg, part, charset,
fallback))
Mailfromd Manual:
Message digests are specially formatted messages that contain certain number of mail messages, encapsulated using the method described in RFC 934. Such digests are often used in mailing lists to reduce the frequency of sending mails. Messages of this format are also produced by the forward function in most MUA’s.
The usual way to handle a message digest in MFL is to convert it first to a MIME message, and then to use functions for accessing its parts (see MIME functions).
Converts the message identified by the descriptor nmsg to a multi-part message. Returns a descriptor of the created message.
Optional argument flags controls the behavior of the bursting agent. It is a bitwise OR of error action and bursting flags.
Error action defines what to do if a part of the digest is
not in RFC822 message format. If it is ‘BURST_ERR_FAIL’ (the
default), the function will raise the ‘e_format’ exception. If
onerr is ‘BURST_ERR_IGNORE’, the improperly formatted part
will be ignored. Finally, the value ‘BURST_ERR_BODY’ instructs
message_burst to create a replacement part with empty headers
and the text of the offending part as its body.
Bursting flags control various aspects of the agent behavior. Currently only one flag is defined, ‘BURST_DECODE’, which instructs the agent to decode any MIME parts (according to the ‘Content-Transfer-Encoding’ header) it encounters while bursting the message.
Parts of a message digest are separated by so-called encapsulation boundaries, which are in essence lines beginning with at least one dash followed by a non-whitespace character. A dash followed by a whitespace serves as a byte-stuffing character, a sort of escape for lines which begin with a dash themselves. Unfortunately, there are mail agents which do not follow byte-stuffing rules and pass lines beginning with dashes unmodified into resulting digests. To help handle such cases a global variable is provided which controls how much dashes should the line begin with for it to be recognized as an encapsulation boundary.
Minimal number of consecutive dashes an encapsulation boundary must begin with.
The default is 2.
The following example shows a function which saves all parts of a digest message to separate disk files. The argument orig is a message descriptor. The resulting files are named by concatenating the string supplied by the stem argument and the ordinal number (1-based) of the message part.
func burst_digest(number orig, string stem)
do
number msg message_burst(orig)
number nparts message_count_parts(msg)
loop for number i 1,
while i <= nparts,
set i i + 1
do
number part message_get_part(msg, i)
number out open(sprintf('>%s%02d', stem, i))
message_to_stream(out, part)
done
message_close(msg)
done
Mailfromd Manual:
Place the message to the quarantine queue, using text as explanatory reason.
Mailfromd Manual:
Opens connection to the callout server listening at url. Returns the descriptor of the connection.
Closes the connection. fd is the file descriptor returned by
the previous call to callout_open.
Instructs the callout server identified by fd (a file descriptor
returned by a previous call to callout_open) to verify the
validity of the email. Optional rest argument supplies
additional parameters for the server.
Possible return values:
0Success. The email is found to be valid.
e_not_foundemail does not exist.
e_temp_failureThe email validity cannot be determined right now, e.g. because remote SMTP server returned temporary failure. The caller should retry verification later.
e_failureSome error occurred.
The function will throw the e_callout_proto exception if the
remote host doesn’t speak the correct callout protocol.
Upon return, callout_do modifies the following variables:
last_poll_hostHost name or IP address of the last polled SMTP server.
last_poll_greetingInitial SMTP reply from the last polled host.
last_poll_heloThe reply to the HELO (EHLO) command, received from the
last polled host.
last_poll_sentLast SMTP command sent to the polled host. If nothing was
sent, last_poll_sent contains the string ‘nothing’.
last_poll_recvLast SMTP reply received from the remote host. In case of multi-line replies, only the first line is stored. If nothing was received the variable contains the string ‘nothing’.
The default callout server is defined by the callout-url
statement in the configuration file, or by the callout
statement in the server milter section (see configuring default callout server. The following functions operate on that server.
Returns URL of the default callout server.
Verifies the validity of the email using the default callout server.
Mailfromd Manual:
The following functions are wrappers over the callout functions described in the previous section. They are provided for backward compatibility.
These functions are defined in the module poll.mf, which you must require prior to using any of them.
Poll SMTP host ip for email address email,
using domain as EHLO domain and mailfrom as
MAIL FROM. Returns 0 or 1 depending on the result of the test.
In contrast to the strictpoll function, this function does not use
cache database and does not fall back to polling MX servers if the
main poll tempfails. The function can throw one of the following
exceptions: e_failure, e_temp_failure.
Poll MXs of the domain for email address email, using
domain as EHLO domain and mailfrom as MAIL
FROM address. Returns 0 or 1 depending on the result of the test.
In contrast to the stdpoll function, _pollmx does
not use cache database and does not fall back to polling the ip
if the poll fails. The function can throw one of the following
exceptions: e_failure, e_temp_failure.
Performs standard poll for email, using domain as
EHLO domain and mailfrom as MAIL FROM address.
Returns 0 or 1 depending on the result of the test. Can raise one of
the following exceptions: e_failure, e_temp_failure.
In on statement context, it is synonymous to poll
without explicit host.
Performs strict poll for email on host host.
See the description of stdpoll for the detailed information.
In on context, it is synonymous to poll host host.
The mailfrom argument can be a comma-separated list of email addresses, which can be useful for servers that are unusually picky about sender addresses. It is advised, however, that this list always contain the ‘<>’ address. For example:
_pollhost($client_addr, $f, "domain", "postmaster@my.net,<>")
See also mail-from-address.
Before returning, all described functions set the following built-in variables:
| Variable | Contains |
|---|---|
| last_poll_host | Host name or IP address of the last polled host. |
| last_poll_sent | Last SMTP command, sent to this host. If nothing was sent, it contains literal string ‘nothing’. |
| last_poll_recv | Last SMTP reply received from this host. In case of multi-line replies, only the first line is stored. If nothing was received the variable contains the string ‘nothing’. |
| cache_used | 1 if cached data were used instead of
polling, 0 otherwise. This variable is set by stdpoll
and strictpoll. If it equals 1, none of the above
variables are modified. See cache_used example, for an example. |
Table 5.1: Variables set by polling functions
Mailfromd Manual:
Following functions operate on IPv4 addresses and CIDRs.
Converts the number n, from host to network byte order. The argument n is treated as an unsigned 32-bit number.
Converts the number n, from network to host byte order. The argument n is treated as an unsigned 32-bit number.
The argument n is treated as an unsigned 16-bit number. The function converts this number from network to host order.
The argument n is treated as an unsigned 16-bit number. The function converts this number from host to network order.
Converts the Internet host address s from the standard numbers-and-dots notation into the equivalent integer in host byte order.
inet_aton("127.0.0.1") ⇒ 2130706433
The numeric data type in MFL is signed, therefore on machines with 32 bit integers, this conversion can result in a negative number:
inet_aton("255.255.255.255") ⇒ -1
However, this does not affect arithmetical operations on IP addresses.
Converts the Internet host address n, given in host byte order to string in standard numbers-and-dots notation:
inet_ntoa(2130706433) ⇒ "127.0.0.1"
Convert number of masked bits n to IPv4 netmask:
inet_ntoa(len_to_netmask(24)) ⇒ 255.255.255.0 inet_ntoa(len_to_netmask(7)) ⇒ 254.0.0.0
If n is greater than 32 the function raises e_range
exception.
Convert IPv4 netmask mask into netmask length (number of bits preserved by the mask):
netmask_to_len(inet_aton("255.255.255.0")) ⇒ 24
netmask_to_len(inet_aton("254.0.0.0")) ⇒ 7
This function is defined in the module match_cidr.mf (see Modules).
It returns true if the IP address ip pertains to the
IP range cidr. The first argument, ip, is a string
representation of an IP address. The second argument, cidr, is
a string representation of a IP range in CIDR notation, i.e.
"A.B.C.D/N", where A.B.C.D is an IPv4
address and N specifies the prefix length – the number of
shared initial bits, counting from the left side of the address.
The following example will reject the mail if the IP address of
the sending machine does not belong to the block 10.10.1.0/19:
if not match_cidr(${client_addr}, "10.10.1.0/19")
reject
fi
Mailfromd Manual:
MFL offers two sets of functions for querying the Domain Name
System. The dns_query function and associated
dns_reply_ functions provide a generalized DNS API.
Other functions provide a simplified API.
Mailfromd Manual:
This function looks up the domain name name. The type argument specifies type of the query to perform. On success, the function returns DNS reply descriptor, a non-negative integer number identifying the reply. It can then be passed to any of the ‘dns_reply_’ functions discussed below in order to retrieve the information from it.
If no matching records were found, the function returns ‘-1’.
On error, it throws a corresponding exception.
The type argument is one of the following constants (defined in the module ‘dns’):
Query the ‘A’ record. The domain should be the hostname to look up.
Query the ‘NS’ records.
Query the ‘PTR’ record. The domain address should be the IP address in dotted-quad form.
Query the ‘MX’ records.
Query the ‘TXT’ records.
If the query returns multiple RR sets, the optional argument sort controls whether they should be returned in the same order as obtained from the DNS (0, the default), or should be sorted (1).
The optional argument resolve is consulted for type
DNS_TYPE_MX and DNS_TYPE_NS. If it is 1, the
DNS_TYPE_MX query will return host names of the MX servers (by
default, it returns IP addresses) and the DNS_TYPE_NS query
will return IP addresses of the name servers (by default it returns
hostnames).
To extract actual data from the dns_query return value, use the
functions dns_reply_count and dns_reply_string. The
usual processing sequence is:
require dns
# Send the query and save the reply descriptor
set n dns_query(DNS_TYPE_NS, domain_name)
if n >= 0
# If non-empty set is returned, iterate over each value in it:
loop for set i 0,
while i < dns_reply_count(n),
set i i + 1
do
# Get the actual data:
echo dns_reply_string(n, i)
done
# Release the memory associated with the reply.
dns_reply_release(n)
fi
Release the memory associated with the reply rd. If rd is -1, the function does nothing.
Return the number of records in the reply rd. For convenience, if rd is -1, the function returns 0. If rd is negative (excepting -1), a ‘e_failure’ exception is thrown.
Returns nth record from the DNS reply rd.
Returns nth record from the DNS reply rd, if the reply contains IP addresses.
Mailfromd Manual:
These functions are implemented in two layers: primitive built-in functions which raise exceptions if the lookup fails, and library calls that are warranted to always return meaningful value without throwing exceptions.
The built-in layer is always available. The library calls become available after requesting the dns module (see Modules):
require dns
Returns a whitespace-separated list of IP addresses (A
records) for domain.
Returns a whitespace-separated list of domain names (PTR
records) for the IPv4 address ipstr.
Returns a whitespace-separated list of ‘MX’ names (if ip is not
given or if it is 0) or ‘MX’ IP addresses (if
ip!=0)) for domain. Within the returned
string, items are sorted in order of increasing ‘MX’ priority.
If domain has no ‘MX’ records, an empty string is returned.
If the DNS query fails, getmx raises an appropriate
exception.
Examples:
getmx("mafra.cz") ⇒ "smtp1.mafra.cz smtp2.mafra.cz relay.iol.cz"
getmx("idnes.cz") ⇒ "smtp1.mafra.cz smtp2.mafra.cz relay.iol.cz"
getmx("gnu.org") ⇒ "mx10.gnu.org mx20.gnu.org"
getmx("org.pl") ⇒ ""
Notes:
getmx(domain) can
differ from that obtained from getmx(domain, 1), e.g.:
getmx("aol.com")
⇒ mailin-01.mx.aol.com mailin-02.mx.aol.com
mailin-03.mx.aol.com mailin-04.mx.aol.com
getmx("aol.com", 1)
⇒ 64.12.137.89 64.12.137.168 64.12.137.184
64.12.137.249 64.12.138.57 64.12.138.88
64.12.138.120 64.12.138.185 205.188.155.89
205.188.156.185 205.188.156.249 205.188.157.25
205.188.157.217 205.188.158.121 205.188.159.57
205.188.159.217
dns_query.
If you intend to iterate over returned values, better use
dns_query directly, e.g. instead of doing
string_list_iterate(getmx(domain), ` ', MX, `do_something(MX)')
use
set n dns_query(DNS_TYPE_MX, domain)
if n >= 0
loop for set i 0,
while i < dns_reply_count(n),
set i i + 1
do
do_something(dns_reply_string(n, i))
done
dns_reply_release(n)
fi
See dns_query, for details about the dns_query function and
associated dns_reply_* calls.
It will most probably be removed in future releases, when array data types are implemented.
Returns true if the domain name given by its argument
has any ‘MX’ records.
If the DNS query fails, this function throws failure or
temp_failure.
Returns true if the domain name given by its argument
has any ‘MX’ records.
Otherwise, if domain has no ‘MX’s or if the DNS query fails,
hasmx returns false.
The ip argument should be a string representing an IP address in dotted-quad notation. The function returns the canonical name of the host with this IP address obtained from DNS lookup. For example
primitive_hostname (${client_addr})
returns the fully qualified domain name of the host represented by Sendmail variable ‘client_addr’.
If there is no ‘PTR’ record for ip, primitive_hostname
raises the exception e_not_found.
If DNS query fails, the function raises failure or
temp_failure, depending on the character of the failure.
The ip argument should be a string representing an IP address in dotted-quad notation. The function returns the canonical name of the host with this IP address obtained from DNS lookup.
If there is no ‘PTR’ record for ip, or if the lookup fails, the function returns ip unchanged.
The previous mailfromd versions used the following
paradigm to check if an IP address resolves:
if hostname(ip) != ip
...
The domain argument is any valid domain name, the host is a host name or IP address.
The function returns true if host is one of the ‘MX’
records for the domain.
If domain has no ‘MX’ records, primitive_ismx raises
exception e_not_found.
If DNS query fails, the function raises failure or
temp_failure, depending on the character of the failure.
The domain argument is any valid domain name, the host is a host name or IP address.
The function returns true if host is one of the ‘MX’
records for the domain. Otherwise it returns false.
If domain has no ‘MX’ records, or if the DNS query fails, the
function returns false.
Reverse of primitive_hostname. The primitive_resolve function
returns the IP address for the host name specified by host
argument. If host has no A records, the function raises the
exception e_not_found.
If DNS lookup fails, the function raises failure or
temp_failure, depending on the character of the failure.
If the optional domain argument is given, it will be appended to host (with an intermediate dot), before querying the DNS. For example, the following two expressions will return the same value:
primitive_resolve("puszcza.gnu.org.ua")
primitive_resolve("puszcza", "gnu.org.ua")
There is a considerable internal difference between one-argument and
two-argument forms of primitive_resolve: the former
queries DNS for an ‘A’ record, whereas the latter
queries it for any record matching host in the domain
domain and then selects the most appropriate one. For example,
the following two calls are equivalent:
primitive_hostname("213.130.0.22")
primitive_resolve("22.0.130.213", "in-addr.arpa")
This makes it possible to use primitive_resolve for querying
DNS black listing domains. See match_dnsbl, for a
working example of this approach. See also match_rhsbl, for
another practical example of the use of the two-argument form.
Reverse of hostname. The resolve function
returns IP address for the host name specified by host
argument. If the host name cannot be resolved, or a DNS failure
occurs, the function returns ‘"0"’.
This function is entirely equivalent to primitive_resolve
(see above), except that it never raises exceptions.
Tests whether the DNS reverse-mapping for ip exists and correctly points to a domain name within a particular domain.
First, it obtains all PTR records for ip. Then, for each record returned, a look up for A records is performed and IP addresses of each record are compared against ip. The function returns true if a matching A record is found.
Returns ‘True’ if the domain domain has at least one ‘NS’ record. Throws exception if DNS lookup fails.
Returns ‘True’ if the domain domain has at least one ‘NS’ record. Returns ‘False’ if there are no ‘NS’ records or if the DNS lookup fails.
Returns a whitespace-separated list of all the ‘NS’ records for the domain domain. Optional parameters resolve and sort control the formatting. If resolve is 0 (the default), the resulting string will contain IP addresses of the NS servers. If resolve is not 0, hostnames will be returned instead. If sort is 1, the returned items will be sorted.
If the DNS query fails, getns raises an appropriate
exception.
Notes:
dns_query.
If you intend to iterate over returned values, better use
dns_query directly, e.g. instead of doing
string_list_iterate(getns(domain), ` ', NS, `do_something(NS)')
use
set n dns_query(DNS_TYPE_NS, domain)
if n >= 0
loop for set i 0,
while i < dns_reply_count(n),
set i i + 1
do
do_something(dns_reply_string(n, i))
done
dns_reply_release(n)
fi
See dns_query, for details about the dns_query function and
associated dns_reply_* calls.
It will most probably be removed in future releases, when array data types are implemented.
Mailfromd Manual:
The geolocation functions allow you to identify the country where
the given IP address or host name is located. These functions are
available only if the libmaxminddb library is installed and
mailfromd is compiled with the ‘GeoIP2’ support.
The libmaxminddb library is distributed by ‘MaxMind’ under
the terms of the Apache License Version 2.0. It is available
from https://dev.maxmind.com/geoip/geoip2/downloadable/#MaxMind_APIs.
Historically, mailfromd supports also the legacy
‘GeoIP’ library. If you are interested in it, please refer to
Legacy geoip support.
Opens the geolocation database file filename. The database must be in GeoIP2 format.
If the database cannot be opened, geoip2_open throws the
e_failure exception.
If this function is not called, geolocation functions described below will try to open the database file ‘/usr/share/GeoIP/GeoLite2-City.mmdb’.
Returns the name of the geolocation database currently in use.
The geolocation database for each IP address, which serves as a look up key, stores a set of items describing this IP. This set is organized as a map of key-value pairs. Each key is a string value. A value can be a scalar, another map or array of values. Using JSON notation, the result of a look up in the database might look as:
{
"country":{
"geoname_id":2921044,
"iso_code":"DE",
"names":{
"en": "Germany",
"de": "Deutschland",
"fr":"Allemagne"
},
},
"continent":{
"code":"EU",
"geoname_id":6255148,
"names":{
"en":"Europe",
"de":"Europa",
"fr":"Europe"
}
},
"location":{
"accuracy_radius":200,
"latitude":49.4478,
"longitude":11.0683,
"time_zone":"Europe/Berlin"
},
"city":{
"geoname_id":2861650,
"names":{
"en":"Nuremberg",
"de":"Nürnberg",
"fr":"Nuremberg"
}
},
"subdivisions":[{
"geoname_id":2951839,
"iso_code":"BY",
"names":{
"en":"Bavaria",
"de":"Bayern",
"fr":"Bavière"
}
}
}
Each particular data item in such structure is identified by its
search path, which is a dot-delimited list of key names leading
to that value. For example, using the above map, the name of the city
in English can be retrieved using the key city.names.en.
Looks up the IP address ip in the geolocation database. If found, returns data item identified by the search path path.
The function can throw the following exceptions:
The ip was not found in the database.
The path does not exist the returned map.
General error occurred. E.g. the database cannot be opened, ip is not a valid IP address, etc.
Looks up the ip in the database and returns entire data set associated with it, formatted as a JSON object. If the optional parameter indent is supplied and is greater than zero, it gives the indentation for each nesting level in the JSON object.
Applications may test whether the GeoIP2 support is present and
enable the corresponding code blocks conditionally, by testing if
the ‘WITH_GEOIP2’ m4 macro is defined. For example, the
following code adds to the message the ‘X-Originator-Country’
header, containing the 2 letter code of the country where the client
machine is located. If mailfromd is compiled without
‘GeoIP’ support, it does nothing:
m4_ifdef(`WITH_GEOIP2',`
try
do
header_add("X-Originator-Country", geoip2_get($client_addr,
'country.iso_code'))
done
catch e_not_found or e_range
do
pass
done
')
Mailfromd Manual:
For compatibility with older releases, mailfromd supports
the legacy ‘GeoIP’ library. This support is going to be removed
in the next release, so its use is not recommended. Please use
‘GeoIP2’ instead.
The support for the legacy GeoIP library is available if
mailfromd is compiled with the ‘GeoIP’ support (the
--with-geoip configure option). The m4 macro
‘WITH_GEOIP’ is defined if it is so.
The legacy GeoIP is distributed by ‘MaxMind’ under the terms of the GNU Lesser General Public License. The library is available from http://www.maxmind.com/app/c.
Look up the ‘ISO 3166-1’ country code corresponding to the IP address ip. If tlc is given and is not zero, return the 3 letter code, otherwise return the 2 letter code.
Look up the ‘ISO 3166-1’ country code corresponding to the host name name. If tlc is given and is not zero, return the 3 letter code, otherwise return the 2 letter code.
If it is impossible to locate the country, both functions raise the
e_not_found exception. If an error internal to the
‘GeoIP’ library occurs, they raise the e_failure
exception.
Applications may test whether the GeoIP support is present and
enable corresponding code blocks conditionally, by testing if
the ‘WITH_GEOIP’ m4 macro is defined. For example, the
following code adds to the message the ‘X-Originator-Country’
header, containing the 2 letter code of the country where the client
machine is located. If mailfromd is compiled without
‘GeoIP’ support, it does nothing:
m4_ifdef(`WITH_GEOIP',`
header_add("X-Originator-Country", geoip_country_code_by_addr($client_addr))
')
Mailfromd Manual:
The functions described below provide a user interface to DBM databases.
Each DBM database is a separate disk file that keeps key/value pairs. The interface allows to retrieve the value corresponding to a given key. Both ‘key’ and ‘value’ are null-terminated character strings. To lookup a key, it is important to know whether its length includes the terminating null byte. By default, it is assumed that it does not.
Another important database property is the file mode of the database file. The default file mode is ‘640’ (i.e. ‘rw-r----’, in symbolic notation).
Both properties can be configured using the dbprop pragma:
#pragma dbprop pattern prop [prop]
The pattern is the database name or shell-style globbing
pattern. Properties defined by that pragma apply to each database
whose name matches this pattern. If several dbprop pragmas
match the database name, the one that matches exactly is preferred.
The rest of arguments define properties for that database. The valid values for prop are:
Setting ‘null’ property is necessary, for databases created with
makemap -N hash command.
640 rw-r----
For example, consider the following pragmas:
#pragma dbprop /etc/mail/whitelist.db 640
It tells that the database file whitelist.db has privileges ‘640’ and do not include null in the key length.
Similarly, the following pragma:
#pragma dbprop `/etc/mail/*.db' null 600
declares that all database files in directory /etc/mail have
privileges ‘640’ and include null terminator in the key
length. Notice, the use of m4 quoting characters in
the example below. Without them, the sequence ‘/*’ would have
been taken as the beginning of a comment.
Additionally, for compatibility with previous versions (up to 5.0), the terminating null property can be requested via an optional argument to the database functions (in description below, marked as null).
Looks up key in the DBM file db and returns
true if it is found.
See above for the meaning of null.
See whitelisting, for an example of using this function.
Looks up key in the database db and returns the value associated with it. If the key is not found returns default, if specified, or empty string otherwise.
See above for the meaning of null.
Inserts in the database a record with the given key and value. If a record with the given key already exists, its value is replaced with the supplied one.
See above for the meaning of null. Optional mode allows
to explicitly specify the file mode for this database. See also
#pragma dbprop, described above.
This is an improved variant of dbput, which provides a
better control on the actions to take if the key already exists in the
database. Namely, if replace is ‘True’, the old value is
replaced with the new one. Otherwise, the ‘e_exists’ exception
is thrown.
Delete from the database the record with the given key. If there are no such record, return without signalling error.
If the optional null argument is given and is not zero, the terminating null character will be included in key length.
Optional mode allows to explicitly specify the file mode for
this database. See also #pragma dbprop, described above.
The functions above have also the corresponding exception-safe interfaces, which return cleanly if the ‘e_dbfailure’ exception occurs. To use these interfaces, request the safedb module:
require safedb
The exception-safe interfaces are:
This is an exception-safe interface to dbmap. If a
database error occurs while attempting to retrieve the record,
safedbmap returns default or ‘0’, if it is
not defined.
This is an exception-safe interface to dbget. If a
database error occurs while attempting to retrieve the record,
safedbget returns default or empty string, if it is
not defined.
This is an exception-safe interface to dbput. If a
database error occurs while attempting to retrieve the record,
the function returns without raising exception.
This is an exception-safe interface to dbdel. If a
database error occurs while attempting to delete the record,
the function returns without raising exception.
The verbosity of ‘safedb’ interfaces in case of database error is
controlled by the value of safedb_verbose variable. If it is
‘0’, these functions return silently. This is the default
behavior. Otherwise, if safedb_verbose is not ‘0’, these
functions log the detailed diagnostics about the database error and
return.
The following functions provide a sequential access to the contents of a DBM database:
Start sequential access to the database name. The return value is an opaque identifier, which is used by the remaining sequential access functions. This number is ‘0’ if the database is empty.
Select next record form the database. The argument dn is the
access identifier, returned by a previous call to dbfirst or
dbnext.
Returns new access identifier. This number is ‘0’ if all records in the database have been visited.
The usual approach for iterating over all records in a database dbname is:
loop for number dbn dbfirst(dbname)
do
…
done while dbnext(dbn)
The following two functions can be used to access values of the
currently selected database record. Their argument, dn, is the
access identifier, returned by a previous call to dbfirst or
dbnext.
Return the key from the selected database record.
Return the value from the selected database record.
The fmt argument is a database format identifier
(see Database Formats). If it is valid, the function returns the
expiration interval for that format. Otherwise, db_expire_interval raises the
e_not_found exception.
The fmtid argument is a database format identifier
(see Database Formats). The function returns the file name
for that format. If fmtid does not match any known format,
db_name raises the e_not_found exception.
Returns the flag indicating whether the cache database fmtid
is currently enabled. If fmtid does not match any known format,
db_name raises the e_not_found exception.
Enables the cache database fmtid if enable is ‘True’, or disables it otherwise. For example, to disable DNS caching, do:
db_set_active("dns", 0)
Returns true if the string domain is found in one of
relayed domain files (see relayed-domain-file). The
usual construct is:
if relayed(hostname(${client_addr}))
…
which yields true if the IP address from Sendmail variable
‘client_addr’ is relayed by the local machine.
Mailfromd Manual:
Checks whether the calling process can access the file pathname. If pathname is a symbolic link, it is dereferenced. The function returns ‘True’ if the file can be accessed and ‘False’ otherwise22.
Symbolic values for mode are provided in module status:
Tests for the existence of the file.
Tests whether the file exists and grants read permission.
Tests whether the file exists and grants write permission.
Tests whether the file exists and grants execute permission.
Searches the environment list for the variable name and returns its value. If the variable is not defined, the function raises the exception ‘e_not_found’.
Return the host name of this machine.
If the optional fqn is given and is ‘true’, the function will attempt to return fully-qualified host name, by attempting to resolve it using DNS.
Return the domain name of this machine. Note, that it does not necessarily coincide with the actual machine name in DNS.
Depending on the underlying ‘libc’ implementation, this call may
return empty string or the string ‘(none)’. Do not rely on it to
get the real domain name of the box mailfromd runs on, use
localdomain (see below) instead.
Return the local domain name of this machine.
This function first uses getdomainname to make a first guess.
If it does not return a meaningful value, localdomain calls
gethostname(1) to determine the fully qualified host name of
the machine, and returns its domain part.
To use this function, require the localdomain module
(see Modules), e.g.: require localdomain.
Return the time since the Epoch (00:00:00 UTC, January 1, 1970), measured in seconds.
Formats the time timestamp (seconds since the Epoch) according
to the format specification format. Ordinary characters placed
in the format string are copied to the output without conversion.
Conversion specifiers are introduced by a ‘%’ character.
See Time and Date Formats, for a detailed description of the
conversion specifiers. We recommend using single quotes
around fmt to prevent ‘%’ specifiers from being interpreted
as Mailfromd variables (See Literals, for a
discussion of quoted literals and variable interpretation within
them).
The timestamp argument can be a return value of time
function (see above).
For example:
strftime('%Y-%m-%d %H:%M:%S %Z', 1164477564)
⇒ 2006-11-25 19:59:24 EET
strftime('%Y-%m-%d %H:%M:%S %Z', 1164477564, 1)
⇒ 2006-11-25 17:59:24 GMT
This function returns system information formatted according to the format specification format. Ordinary characters placed in the format string are copied to the output without conversion. Conversion specifiers are introduced by a ‘%’ character. The following conversions are defined:
Name of this system.
Name of this node within the communications network to which this node is attached. Note, that it does not necessarily coincide with the actual machine name in DNS.
Kernel release.
Kernel version.
Name of the hardware type on which the system is running.
For example:
uname('%n runs %s, release %r on %m')
⇒ "Trurl runs Linux, release 2.6.26 on i686"
Notice the use of single quotes.
Unlinks (deletes) the file name. On error, throws the
e_failure exception.
The function system executes a command specified in str
by calling /bin/sh -c string, and returns -1 on error or
the return status of the command otherwise.
Sleep for secs seconds. If optional usec argument is given, it specifies additional number of microseconds to wait for. For example, to suspend execution of the filter for 1.5 seconds:
sleep(1,500000)
This function is intended mostly for debugging and experimental purposes.
Set the umask to mask & 0777. Return the previous value of the mask.
Mailfromd Manual:
Look for the user name (getpwnam) or user ID uid
(getpwuid) in the system password database and return the
corresponding record, if found. If not found, raise the
‘e_not_found’ exception.
The returned record consists of six fields, separated by colon sign:
uname:passwd:uid:gid:gecos:dir:shell
| Field | Meaning |
|---|---|
| uname | user name |
| passwd | user password |
| uid | user ID |
| gid | group ID |
| gecos | real name |
| dir | home directory |
| shell | shell program |
For example:
getpwnam("gray")
⇒ "gray:x:1000:1000:Sergey Poznyakoff:/home/gray:/bin/bash"
Following two functions can be used to test for existence of a key in the user database:
Return ‘true’ if name (or uid) is found in the system user database.
Mailfromd Manual:
‘Sieve’ is a powerful mail filtering language, defined in
RFC 3028. Mailfromd supports an extended form
of this language. For a description of the language and available
extensions, see Sieve Language in GNU Mailutils Manual.
Compile the Sieve program script and execute it over the message identified by the descriptor nmsg.
Optional flags modify the behavior of the function. It is a
bit-mask field, consisting of a bitwise or of one or more of
the following flags, defined in sieve.mf:
MF_SIEVE_FILEThe script argument specifies the name of a Sieve program file. This is the default.
MF_SIEVE_TEXTThe script argument is a string containing entire Sieve program. Optional arguments file and line can be used to fix source locations in Sieve diagnostic messages (see below).
MF_SIEVE_LOGLog every executed ‘Sieve’ action.
MF_SIEVE_DEBUG_TRACETrace execution of ‘Sieve’ tests.
MF_SIEVE_DEBUG_INSTRLog every instruction, executed in the compiled ‘Sieve’ code. This produces huge amounts of output and is rarely useful, unless you suspect some bug in ‘Sieve’ implementation and wish to trace it.
For example, MF_SIEVE_LOG|MF_SIEVE_DEBUG_TRACE enables logging
‘Sieve’ actions and tests.
The sieve function returns true if the message was
accepted by the script program, and false otherwise.
Here, the word accepted means that some form of ‘KEEP’
action (see Actions in GNU Mailutils
Manual) was executed over the message.
While executing the Sieve script, Sieve environment (RFC 5183) is initialized as follows:
The domain name of the server Sieve is running on.
Host name of the server Sieve is running on.
The string ‘MTA’.
The string ‘GNU Mailutils’.
The string ‘pre’.
Defined to the value of ‘client_ptr’ macro, if it was required.
Defined to the value of ‘client_addr’ macro, if it was required.
The version of GNU Mailutils.
The following example discards each message not accepted by the ‘Sieve’ program /etc/mail/filter.siv:
require 'sieve'
group eom
do
if not sieve(current_message(), "/etc/mail/filter.siv", MF_SIEVE_LOG)
discard
fi
done
The Sieve program can be embedded in the MFL filter, as shown in the example below:
require 'sieve'
prog eom
do
if not sieve(current_message(),
"require \"fileinto\";\n"
"fileinto \"/tmp/sieved.mbox\";",
MF_SIEVE_TEXT | MF_SIEVE_LOG)
discard
fi
done
In such cases, any Sieve diagnostics (error messages, traces, etc.)
will be marked with the locations relative to the line where the call
to sieve appears. For example, the above program produces the
following in the log:
prog.mf:7: FILEINTO; delivering into /tmp/sieved.mbox
Notice, that the line number correctly refers to the line where the
fileinto action appears in the source. However, there are
cases where the reported line number is incorrect. This happens,
for instance, if script is a string variable defined elsewhere.
To handle such cases, sieve accepts two optional parameters
which are used to compute the location in the Sieve program. The
file parameter specifies the file name where the definition of
the program appears, and the line parameter gives the number of
line in that file where the program begins. For example:
require 'sieve'
const sieve_prog_line __line__ + 2
string sieve_prog <<EOT
require "fileinto";
fileinto "/tmp/sieved.mbox";
EOT
prog eom
do
if not sieve(current_message(),
sieve_prog, MF_SIEVE_TEXT | MF_SIEVE_LOG,
__file__, sieve_prog_line)
discard
fi
done
The actual Sieve program begins two lines below the
sieve_prog_line constant definition, which is reflected in its
initialization.
Mailfromd Manual:
A set of functions is defined for interfacing with other filters via
TCP. Currently implemented are interfaces with
SpamAssassin spamd daemon and with
ClamAV anti-virus.
Both interfaces work much the same way: the remote filter is
connected and the message is passed to it. If the remote filter
confirms that the message matches its requirements, the function
returns true. Notice that in practice that means that such a
message should be rejected or deferred.
The address of the remote filter is supplied as the second argument in the form of a standard URL:
proto://path[:port]
The proto part specifies the connection protocol. It should be ‘tcp’ for the TCP connection and ‘file’ or ‘socket’ for the connection via UNIX socket. In the latter case the proto part can be omitted. When using TCP connection, the path part gives the remote host name or IP address and the optional port specifies the port number or service name to use. For example:
# connect to ‘remote.filter.net’ on port 3314: tcp://remote.filter.net:3314 # the same, using symbolic service name (must be defined in # /etc/services): tcp://remote.filter.net:spamd # Connect via a local UNIX socket (equivalent forms): /var/run/filter.sock file:///var/run/filter.sock socket:///var/run/filter.sock
The description of the interface functions follows.
Mailfromd Manual:
Send the message msgt to the SpamAssassin daemon (spamd)
listening on the given url. The command argument
identifies what kind of processing is needed for the message. Allowed
values are:
Process the message and return 1 or 0 depending on whether it is
diagnosed as spam or not. Store SpamAssassin keywords in the global
variable sa_keywords (see below).
Process the message and return 1 or 0 depending on whether it is
diagnosed as spam or not. Store entire SpamAssassin report in the
global variable sa_keywords.
Learn the supplied message as spam.
Learn the supplied message as ham.
Forget any prior classification of the message.
The second argument, prec, gives the precision, in decimal
digits, to be used when converting SpamAssassin diagnostic data and
storing them into mailfromd variables.
The floating point SpamAssassin data are converted to the integer
mailfromd variables using the following relation:
var = int(sa-var * 10**prec)
where sa-var stands for the SpamAssassin value and var
stands for the corresponding mailfromd one. int()
means taking the integer part and ‘**’ denotes the exponentiation
operator.
The function returns additional information via the following variables:
sa_scoreThe spam score, converted to integer as described above. To convert
it to a floating-point representation, use sa_format_score
function (see sa_format_score). See also the
example below.
sa_thresholdThe threshold, converted to integer form.
sa_keywordsIf command is ‘SA_SYMBOLS’, this variable contains a string of comma-separated SpamAssassin keywords identifying this message, e.g.:
ADVANCE_FEE_1,AWL,BAYES_99
If command is ‘SA_REPORT’, the value of this variable is a spam report message. It is a multi-line textual message, containing detailed description of spam scores in a tabular form. It consists of the following parts:
The words ‘Content preview’, followed by a colon and an excerpt of the message body.
It has the following form:
Content analysis details: (score points, max required)
where score and max are spam score and threshold in floating point.
The score table is formatted in three columns:
The score, as a floating point number with one decimal digit.
SpamAssassin rule name that contributed this score.
Textual description of the rule
The score table can be extracted from sa_keywords using
sa_format_report_header function (see sa_format_report_header), as illustrated in the example below.
The value of this variable is undefined if command is ‘SA_LEARN_SPAM’, ‘SA_LEARN_HAM’ or ‘SA_FORGET’.
The spamc function can signal the following exceptions:
e_failure if the connection fails, e_url if the supplied
URL is invalid and e_range if the supplied port number
is out of the range 1–65535.
An example of using this function:
prog eom
do
if spamc(current_message(), "tcp://192.168.10.1:3333", 3,
SA_SYMBOLS)
reject 550 5.7.0
"Spam detected, score %sa_score with threshold %sa_threshold"
fi
done
Here is a more advanced example:
prog eom
do
set prec 3
if spamc(current_message(),
"tcp://192.168.10.1:3333", prec, SA_REPORT)
add "X-Spamd-Status" "SPAM"
else
add "X-Spamd-Status" "OK"
fi
add "X-Spamd-Score" sa_format_score(sa_score, prec)
add "X-Spamd-Threshold" sa_format_score(sa_threshold, prec)
add "X-Spamd-Keywords" sa_format_report_header(sa_keywords)
done
Additional interface to the spamc function, provided for
backward compatibility. It is equivalent to
spamc(current_message(), url, prec, command)
If command is not supplied, ‘SA_SYMBOLS’ is used.
Mailfromd Manual:
DSPAM is a statistical spam filter distributed under the terms of the GNU General Public License. It is available from http://dspam.sourceforge.net.
MFL provides an interface to DSPAM functionality if the
libdspam library is installed and mailfromd is linked
with it. The m4 macro ‘WITH_DSPAM’ is defined if it is
so.
The DSPAM functions and definitions become available after requiring the ‘dspam’ module:
require 'dspam'
Analyze a message using DSPAM. The message is identified by its descriptor, passed in the msg argument.
The mode_flags argument controls the function behavior. Its value is
a bitwise OR of operation mode, flag, tokenizer and training
mode. Operation mode defines what dspam is supposed to
do with the message. Its value is either ‘DSM_PROCESS’ if
full processing of the message is intended (the default), or
‘DSM_CLASSIFY’, if the message must only be classified.
Optional flag bits turn on additional functionality. The
‘DSF_SIGNATURE’ bit instructs dspam to create a signature
for the message – a unique string which can subsequently be used to
identify that particular message. Upon return from the function, the
signature is stored in the dspam_signature variable.
The ‘DSF_NOISE’ bit enables Bayesian noise reduction, and ‘DSF_WHITELIST’ enables automatic whitelisting.
Additional flags are available for defining the algorithm to split the message into tokens (tokenizer) and training mode. See flags-dspam, for a complete list of these. All these are optional, any missing values will be read from the DSPAM configuration file.
The configuration file must always be present. Its full file name
must be stored in the global variable dspam_config. There
is no default value, so make sure this variable is initialized. If a
specific profile section should be read, store the name of that
profile in the variable dspam_profile.
When called to process or classify the message, dspam
returns an integer code of the class of the message. The value
‘DSR_ISSPAM’ means that this message was classified as spam. The
value ‘DSR_ISINNOCENT’ means it is a clean (“ham”) message.
The probability and confidence values are returned in global variables
dspam_probability and dspam_confidence. Since
MFL lacks floating-point data type, both variables keep
integers, obtained from the corresponding floating point values by
shifting the decimal point dspam_prec digits to the right and rounding
the resulting value to the nearest integer. The same method
is used in spamc function
(see sa-floating-point-conversion). The default value for
dspam_prec variable is 3. You can use the
sa_format_score function to convert these values to strings
representing floating point numbers, e.g.:
require 'dspam'
require 'sa'
prog eom
do
if dspam(current_message(), DSM_PROCESS | DSM_SIGNATURE)
== DSR_ISSPAM
header_add("X-DSPAM-Result", "Spam")
else
header_add("X-DSPAM-Result", "Innocent")
fi
header_add("X-DSPAM-Probability",
sa_format_score(dspam_probability, dspam_prec))
header_add("X-DSPAM-Confidence",
sa_format_score(dspam_confidence, dspam_prec))
header_add("X-DSPAM-Signature", dspam_signature)
done
Optional class_source argument is used when training the DSPAM classifier. It is a bitwise OR of the message class and message source values. Message class specifies the class this message belongs to. Possible values are ‘DSR_ISSPAM’, for spam messages, and ‘DSR_ISINNOCENT’, for clean messages. Message source informs DSPAM where this message comes from. The value ‘DSS_ERROR’ means the message was previously misclassified by DSPAM. The value ‘DSS_CORPUS’ indicates the message comes from a corpus feed. Finally, the value ‘DSS_INOCULATION’ means that the message is in pristine form, and should be trained as an inoculation. Inoculation is a more intense mode of training, usually used on honeypots.
The following example calls dspam to train the classifier on
the current message if it was sent to a honeypot address, and uses
dspam to analyze the message class otherwise. The
honeypot variable is supposed to be set elsewhere in the code
(e.g. in the ‘envrcpt’ handler):
prog eom
do
number res
if honeypot
set res dspam(current_message(), DSM_PROCESS,
DSR_ISSPAM | DSS_INOCULATION)
discard
else
if dspam(current_message(), DSM_PROCESS | DSM_SIGNATURE)
== DSR_ISSPAM
header_add("X-DSPAM-Result", "Spam")
else
header_add("X-DSPAM-Result", "Innocent")
fi
header_add("X-DSPAM-Probability",
sa_format_score(dspam_probability, dspam_prec))
header_add("X-DSPAM-Confidence"
sa_format_score(dspam_confidence, dspam_prec))
header_add("X-DSPAM-Signature", dspam_signature)
fi
done
Mailfromd Manual:
The tables below summarize flags which can be used in the
mode_flags argument to dspam function. The argument is a
bitwise OR of operation mode, flags,
tokenizer and training mode bits. Only one operation
mode bit can be used. Flags, tokenizer and training mode are
optional. Any number of flags, but no more than one tokenizer type
and one training mode bit are allowed. Missing values will be supplied
from the configuration file.
| Mode | Meaning |
|---|---|
| DSM_PROCESS | Process message |
| DSM_CLASSIFY | Classify message only (do not write changes) |
Table 5.2: DSPAM Operation modes
| Flag | Meaning |
|---|---|
| DSF_SIGNATURE | Create a signature |
| DSF_NOISE | Use Bayesian Noise Reduction |
| DSF_WHITELIST | Use Automatic Whitelisting |
Table 5.3: DSPAM flags
| Constant | Meaning |
|---|---|
| DSZ_WORD | Use WORD tokenizer |
| DSZ_CHAIN | Use CHAIN tokenizer |
| DSZ_SBPH | Use SBPH tokenizer |
| DSZ_OSB | Use OSB tokenizer |
Table 5.4: DSPAM Tokenizer bits
| Mode | Meaning |
|---|---|
| DST_TEFT | Train Everything |
| DST_TOE | Train-on-Error |
| DST_TUM | Train-until-Mature |
Table 5.5: DSPAM Training Modes
Mailfromd Manual:
The tables below summarize flags which can be used in the
class_source argument to dspam function. The argument is a
bitwise OR of classification and source bits. At
most one classification and one source bit can be given. If not
supplied, ‘DSR_NONE|DSS_NONE’ is used.
The classification flags are also used as the return code, as shown in the following table.
| Mode | As return value | As argument |
|---|---|---|
| DSR_NONE | N/A | Classify message |
| DSR_ISSPAM | Message is spam | Learn as spam |
| DSR_ISINNOCENT | Message is innocent | Learn as innocent |
Table 5.6: DSPAM Classification
| Source | Meaning |
|---|---|
| DSS_NONE | No classification source (use only with DSR_NONE) |
| DSS_ERROR | Misclassification by libdspam |
| DSS_CORPUS | Message came from a corpus feed |
| DSS_INOCULATION | Message inoculation |
Table 5.7: DSPAM Source
Mailfromd Manual:
Following global variables affect the behavior of the dspam
function:
Name of the DSPAM configuration file. You must set this variable
prior to calling dspam. There is no default value.
Name of the configuration profile to be used. If empty (the default), use global configuration settings.
Name of the user on behalf of which dspam is called. Default
is empty (no user).
Name of the user group on behalf of which dspam is called. Default
is empty (no group).
Number of decimal digits to retain in the dspam_probability and
dspam_confidence values. See dspam probability and confidence, for more information and examples.
Before returning, dspam stores additional information in the
following variables:
Signature of the classified message. This variable is initialized if ‘DSF_SIGNATURE’ bit is set in the mode_flags argument (see dspam classify example),
Spam probability value converted to integer by shifting decimal point
dspam_prec positions to the right and rounding the resulting number.
See dspam probability and confidence, for more information and examples.
Spam confidence converted to integer using the same algorithm as for
dspam_probability. See dspam probability and confidence,
for more information and examples.
Mailfromd Manual:
Pass the message msg to the ClamAV daemon at url. Return
true if it detects a virus in it. Return virus name in
clamav_virus_name global variable.
The clamav function can signal the following exceptions:
e_failure if failed to connect to the server, e_url if
the supplied URL is invalid and e_range if the
supplied port number is out of the range 1–65535.
An example usage:
prog eom
do
if clamav(current_message(), "tcp://192.168.10.1:6300")
reject 550 5.7.0 "Infected with %clamav_virus_name"
fi
done
Mailfromd Manual:
Returns the mail sending rate for key per sample-interval. Optional min-samples, if supplied, specifies the minimal number of mails needed to obtain the statistics. The default is 2. Optional threshold controls rate database updates. If the observed rate (per sample-interval seconds) is higher than the threshold, the hit counters for that key are not incremented and the database is not updated. Although the threshold argument is optional23, its use is strongly encouraged. Normally, the value of threshold equals the value compared with the return from rate, as in:
if rate("$f-$client_addr", rate_interval, 4, maxrate) > maxrate
tempfail 450 4.7.0 "Mail sending rate exceeded. Try again later"
fi
This function is a low-level interface. Instead of using it directly,
we advise to use the rateok function, described below.
[number min-samples])
To use this function, require the rateok module
(see Modules), e.g.: require rateok.
The rateok function returns ‘True’ if the mail sending
rate for key, computed for the interval of sample-interval
seconds is less than the threshold. Optional min-samples
parameter supplies the minimal number of mails needed to obtain the
statistics. It defaults to 4.
See Sending Rate, for a detailed description of the rateok and
its use. The interval function (see interval) is often
used in the second argument to rateok or rate.
This function implements a classical token bucket filter algorithm.
Tokens are added to the bucket identified by the key at constant
rate of 1 token per sample-interval microseconds, to a maximum
of burst-size tokens. If no bucket is found for the specified key, a
new bucket is created and initialized to contain burst-size
tokens. If the bucket contains cost or more tokens, cost
tokens are removed from it and tbf_rate returns ‘True’.
Otherwise, the function returns ‘False’.
For a detailed description of the Token Bucket Algorithm and its use to limit mail rates, see TBF.
Mailfromd Manual:
Returns ‘True’ if the key is found in the greylist database
(controlled by database greylist configuration file statement,
see conf-database). The argument interval gives the greylisting
interval in seconds. The function stores the number of seconds left to the end
of greylisting period in the global variable
greylist_seconds_left. See Greylisting, for a detailed
explanation.
The function greylist can signal e_dbfailure exception.
Returns ‘True’ if the key is still greylisted. If
‘true’ is returned, the function also stores the number of
seconds left to the end of greylisting period in the global variable
greylist_seconds_left.
This function is available only if Con Tassios implementation of greylisting is used. See greylisting types, for a discussion of available greylisting implementations. See greylist, for a way to switch to Con Tassios implementation.
Mailfromd Manual:
Returns true if the IP address or host name given by
host argument listens on the port number port (default
25).
This function is defined in the module portprobe.
Returns true if authenticity of the user name is
confirmed using mailutils authentication system. See Local Account Verification, for more details.
Returns true if the domain name domain has a
corresponding A record or if it has any ‘MX’ records, i.e. if it
is possible to send mail to it.
To use this function, require the valid_domain module (see Modules):
require valid_domain
Verify if an argument of ‘HELO’ (‘EHLO’) command is valid. To use this function, require the heloarg_test module (see Modules).
Arguments:
‘HELO’ (‘EHLO’) argument. Typically, the value of $s
Sendmail macro;
IP address of the remote client. Typically, the value of
$client_addr Sendmail macro;
IP address of this SMTP server;
The function returns a number describing the result of the test, as described in the following table.
| Code | Meaning |
|---|---|
| HELO_SUCCESS | arg successfully passes all tests. |
| HELO_MYIP | arg is our IP address. |
| HELO_IPNOMATCH | arg is an IP, but it does not match the remote party IP address. |
| HELO_ARGNORESOLVE | arg is an IP, but it does not resolve. |
| HELO_ARGNOIP | arg is in square brackets, but it is not an IP address. |
| HELO_ARGINVALID | arg is not an IP address and does not resolve to one. |
| HELO_MYSERVERIP | arg resolves to our server IP. |
| HELO_IPMISMATCH | arg does not resolve to the remote client IP address. |
Mailfromd Manual:
The mail sending functions are new interfaces, introduced in version 3.1.
The underlying mechanism for sending mail, called mailer, is specified by --mailer command line option. This global setting can be overridden using the last optional argument to a particular function. In any case, the mailer is specified in the form of a URL.
Mailer URL begins with a protocol specification.
Two protocol specifications are currently supported: ‘sendmail’
and ‘smtp’. The former means to use a
sendmail-compatible program to send mails. Such a program
must be able to read mail from its standard input and must support the
following options:
Do not treat ‘.’ as message terminator.
Use addr as the address of the sender.
Get recipient addresses from the message.
These conditions are met by most existing MTA programs, such
as exim or postfix (to say nothing of
sendmail itself).
Following the protocol specification is the mailer location, which is separated from it with a colon. For the ‘sendmail’ protocol, the mailer location sets the full file name of the Sendmail-compatible MTA binary, for example:
sendmail:/usr/sbin/sendmail
A special form of a sendmail URL, consisting of protocol
specification only (‘sendmail:’) is also allowed. It means
“use the sendmail binary from the _PATH_SENDMAIL
macro in your /usr/include/paths.h file”. This is the default
mailer.
The ‘smtp’ protocol means to use an SMTP server directly. In this case the mailer location consists of two slashes, followed by the IP address or host name of the SMTP server, and, optionally, the port number. If the port number is present, it is separated from the rest of URL by a colon. For example:
smtp://remote.server.net smtp://remote.server.net:24
Sends message msg to the email address to. The value of msg must be a valid RFC 2822 message, consisting of headers and body. Optional argument to can contain several email addresses. In this case the message will be sent to each recipient specified in to. If it is not specified, recipient addresses will be obtained from the message headers.
Other optional arguments are:
Sets the sender address. By default ‘<>’ is used.
The URL of the mailer to use
Sample usage:
set message <<- EOT
Subject: Test message
To: Postmaster <postmaster@gnu.org.ua>
From: Mailfromd <devnull@gnu.org.ua>
X-Agent: %__package__ (%__version__)
Dear postmaster,
This is to notify you that our /etc/mailfromd.mf
needs a revision.
--
Mailfromd filter administrator
EOT
send_mail(message, "postmaster@gnu.org.ua")
A more complex interface to mail sending functions.
Mandatory arguments:
Text of the message to be sent.
Headers for the message.
Optional arguments:
Recipient email addresses.
Sender email address.
URL of the mailer to use.
The above example can be rewritten using send_text as follows:
set headers << -EOT
Subject: Test message
To: Postmaster <postmaster@gnu.org.ua>
From: Mailfromd <devnull@gnu.org.ua>
X-Agent: %__package__ (%__version__)
EOT
set text <<- EOT
Dear postmaster,
This is to notify you that our /etc/mailfromd.mf
needs a revision.
--
Mailfromd filter administrator
EOT
send_text(text, headers, "postmaster@gnu.org.ua")
Send the message identified by descriptor msg (see Message functions).
Optional arguments are:
Recipient email addresses.
Sender email address.
URL of the mailer to use.
This is an experimental interface which will change in the future versions. It sends a message disposition notification (RFC 2298, RFC 1894), of type ‘deleted’ to the email address to. Arguments are:
Recipient email address.
Original sender email address.
Original recipient email address.
Notification text.
Optional arguments:
Message headers
Sender address.
URL of the mailer to use.
Creates DSN message and returns its descriptor. Arguments are:
Original sender email address.
Original recipient email address.
Notification text.
Message headers
Sender address.
Mailfromd Manual:
The functions described in this subsection allow to check whether the given IP address is listed in certain black list DNS zone.
This function looks up address in the DNS blacklist zone zone and checks if the return falls into the given range of IP addresses.
It is intended as a replacement for the Sendmail macros ‘dnsbl’ and ‘enhdnsbl’.
To use match_dnsbl, require the match_dnsbl module
(see Modules).
Arguments:
IP address of the SMTP server to be tested.
FQDN of the DNSbl zone to test against.
The range of IP addresses in CIDR notation or the word ‘ANY’, which stands for ‘127.0.0.0/8’.
The function returns true if dns lookup for address in
the zone dnsbl yields an IP that falls within the range,
specified by cidr. Otherwise, it returns false.
This function raises the following exceptions: e_invip if
address is invalid and e_invcidr if cidr is invalid.
This function checks if the IP address, corresponding to the domain part of email is listed in the RHS DNS blacklist zone zone, and if so, whether its record falls into the given range of IP addresses range.
It is intended as a replacement for the Sendmail macro ‘rhsbl’ by Derek J. Balling.
To use this function, require the match_rhsbl module (see Modules).
Arguments:
E-mail address, whose domain name should be tested (usually, it is
$f)
Domain name of the RHS DNS blacklist zone.
The range of IP addresses in CIDR notation.
Mailfromd Manual:
Sender Policy Framework, or SPF for short, is an
extension to SMTP protocol that allows to identify forged
identities supplied with the MAIL FROM and HELO
commands. The framework is explained in detail in RFC 4408
(http://tools.ietf.org/html/rfc4408) and on the
SPF Project Site. The following
description is a short introduction only, and the users are encouraged
to refer to the original specification for the detailed description of
the framework.
The domain holder publishes an SPF record – a special
DNS resource record that contains a set of rules declaring
which hosts are, and are not, authorized to use a domain name for
HELO and MAIL FROM identities. This resource record is
usually of type TXT.24
The MFL script can verify if the identity matches the
published SPF record by calling check_host function
and analyzing its return code. The function can be called either in
helo or in envfrom handler. Its arguments are:
The IP address of the SMTP client that is emitting the mail.
Usually it is $client_addr.
The domain that provides the sought-after authorization information;
Normally it is the domain portion of the MAIL FROM or
HELO identity.
The MAIL FROM identity.
The HELO identity.
The SMTP domain served by the local server.
The function returns a numeric result code. For convenience, all possible return values are defined as macros in module spf.mf. The table below describes each value along with the recommended actions for it:
NoneA result of None means that no records were published by the domain
or that no checkable sender domain could be determined from the given
identity. The checking software cannot ascertain whether or not the
client host is authorized. Such a message can be subject to
further checks that will decide about its fate.
NeutralThe domain owner has explicitly stated that he cannot or does not
want to assert whether or not the IP address is authorized. This
result must be treated exactly like None; the distinction
between them exists only for informational purposes
PassThe client is authorized to send mail with the given identity. The message can be subject to further policy checks with confidence in the legitimate use of the identity or it can be accepted in the absence of such checks.
FailThe client is not authorized to use the domain in the given identity. The proper action in this case can be to mark the message with a header explicitly stating it is spam, or to reject it outright.
If you choose to reject such mails, we suggest to use reject
550 5.7.1, as recommended by RFC 4408. The reject can return either
a default explanation string, or the one supplied by the domain that
published the SPF records, as in the example below:
reject 550 5.7.1 "SPF check failed:\n%spf_explanation"
(for the description of spf_explanation, see spf_explanation)
SoftFailThe domain believes the host is not authorized but is not willing to
make that strong of a statement. This result code should be treated
as somewhere in between a Fail and a Neutral. It is not
recommended to reject the message based solely on this result.
TempErrorA transient error occurred while performing SPF check. The proper action in this case is to accept or temporarily reject the message. If you choose the latter, we suggest to use SMTP reply code of ‘451’ and DSN code ‘4.4.3’, for example:
tempfail 451 4.4.3
"Transient error while performing SPF verification"
PermErrorThis result means that the domain’s published records could not be
correctly interpreted. This signals an error condition that requires
manual intervention to be resolved, as opposed to the TempError
result.
The following example illustrates the use of SPF
verification in envfrom handler:
require 'status'
require 'spf'
prog envfrom
do
switch check_host($client_addr, domainpart($f), $f, $s)
do
case Fail:
string text ""
if spf_explanation != ""
set text "%text\n%spf_explanation"
fi
reject 550 5.7.1 "SPF MAIL FROM check failed: %text"
case Pass:
accept
case TempError:
tempfail 451 4.4.3
"Transient error while performing SPF verification"
default:
on poll $f do
when success:
accept
when not_found or failure:
reject 550 5.1.0 "Sender validity not confirmed"
when temp_failure:
tempfail 450 4.7.0 "Temporary failure during sender verification"
done
done
done
The SPF support is implemented in MFL in two layers: a built-in layer that provides basic support, and a library layer that provides a convenience wrapper over the library function.
The library layer is implemented in the module spf.mf (see Modules).
The rest of this node describes available SPF functions and variables.
This function is the basic implementation of the check_host
function, defined in RFC 4408, chapter 4. It fetches SPF
records, parses them, and evaluates them to determine whether a
particular host (ip) is or is not permitted to send mail from a
given email address (sender). The function returns an SPF
result code.
Arguments are:
The IP address of the SMTP client that is emitting the mail.
Usually it is $client_addr.
The domain that provides the sought-after authorization information;
Normally it is the domain portion of the MAIL FROM or
HELO identity.
The MAIL FROM identity.
The HELO identity.
The SMTP domain served by the local server.
Before returning the spf_check_host function stores
additional information in global variables:
spf_explanationIf the result code is Fail, this variable contains the
explanation string as returned by the publishing domain, prefixed with
the value of the global variable spf_explanation_prefix.
For example, if spf_explanation_prefix contains ‘The
domain %{o} explains: ’, and the publishing domain
‘example.com’ returns the explanation string ‘Please see
http://www.example.com/mailpolicy.html’, than the value of
spf_explanation will be:
The domain example.com explains: Please see http://www.example.com/mailpolicy.html
(see RFC 4408, chapter 8, for the description of SPF macro facility).
spf_mechanismName of the SPF mechanism that decided about the result code of the SPF record. If one or more ‘include’ or ‘redirect’ mechanisms were traversed before arriving at that mechanism, their values are appended in the reverse order.
Evaluate SPF record record as if it were published
by domain. The rest of arguments are the same as for
spf_check_host above.
This function is designed primarily for testing and debugging purposes. You would hardly need to use it.
The spf_test_record function sets the same global variables
as spf_check_host.
This function implements the check_host function, defined in
RFC 4408, chapter 4. It fetches SPF records, parses them,
and evaluates them to determine whether a particular host (ip)
is or is not permitted to send mail from a given email address
(sender). The function returns an SPF result code.
This function is a wrapper over the built-in spf_check_host.
The arguments are:
The IP address of the SMTP client that is emitting the mail.
Usually it is the same as the value of $client_addr.
The domain that provides the sought-after authorization information;
Normally it is the domain portion of the MAIL FROM or
HELO identity.
The MAIL FROM identity.
The HELO identity.
Converts numeric SPF result code to its string representation.
If check_host (or spf_check_host or
spf_test_record) returned Fail, this variable contains the
explanation string as returned by the publishing domain, prefixed with
the value of the global variable spf_explanation_prefix.
For example, if spf_explanation_prefix contains ‘The
domain %{o} explains: ’, and the publishing domain
‘example.com’ returns the explanation string ‘Please see
http://www.example.com/mailpolicy.html’, than the value of
spf_explanation will be:
The domain example.com explains: Please see http://www.example.com/mailpolicy.html
Set to the name of a SPF mechanism that decided about the result code of the SPF record.
The prefix to be appended to the explanation string before storing
it in the spf_explanation variable. This string can contain
valid SPF macros (see
RFC 4408, chapter 8), for
example:
set spf_explanation_prefix "%{o} explains: "
The default value is ‘""’ (an empty string).
Mailfromd Manual:
DKIM or DomainKeys Identified Mail is an email authentication method that allows recipients to verify if an email was authorized by the owner of the domain that email claims to originate from. It does so by adding a digital signature which is verified using a public key published as a DNS TXT record. For technical details about DKIM, please refer to RFC 6376 (http://tools.ietf.org/html/rfc6376).
MFL provides functions for DKIM signing and verification.
Verifies the message msg (a message descriptor, obtained from
a call to current_message, mailbox_get_message,
message_from_stream or a similar function).
Return value (constants defined in the ‘status’ module):
The message contains one or more ‘DKIM-Signature’ headers and one of them verified successfully.
The message contains one or more ‘DKIM-Signature’ headers, all of which failed to verify.
The message was not signed using DKIM, or the DNS query to obtain the public key failed, or an internal software error occurred during verification.
The following two global variables are always set upon return from this
function: dkim_explanation and dkim_explanation_code.
These can be used to clarify the verification result to the end user.
The variable dkim_signing_algorithm is initialized with the
name of the algorithm used to sign the message.
Upon successful return, the variable dkim_verified_signature is
set to the value of the successfully verified DKIM signature.
Name of the algorithm used to sign the message (either ‘rsa-sha1’ or ‘rsa-sha256’). If the algorithm was not specified (e.g. the signature is malformed), this variable is assigned an empty value.
An explanatory message clarifying the verification result.
A numeric code corresponding to the ‘dkim_explanation’ string. Its possible values are defined in ‘status.mf’:
‘DKIM verification passed’
‘DKIM verification passed’
‘No DKIM signature’
‘internal error’
‘signature syntax error’
‘signature is missing required tag’
According to the DKIM specification, required tags are: a=,
b=, bh=, d=, h=, s=, v=.
‘domain mismatch’
The domain part of the i= tag does not match and is not a
subdomain of the domain listed in the d= tag.
‘incompatible version’
Incompatible DKIM version listed in the v= tag.
‘unsupported signing algorithm’
Either the a= tag of the DKIM signature contains an unsupported
algorithm (currently supported algorithms are: ‘rsa-sha1’ and
‘rsa-sha256’) or this algorithm, while being supported by
mailfromd, is not listed in the h= tag of the public
DKIM key.
‘unsupported query method’
The q= tag of the public DKIM key contains something other than
‘dns/txt’.
‘From field not signed’
‘signature expired’
‘public key unavailable’
‘public key not found’
‘key syntax error’
‘key revoked’
‘body hash did not verify’
‘can't decode b= tag’
Base64 decoding of the b= tag failed.
‘signature did not verify’
‘unsupported public key type’
The k= tag of the public DKIM signature contains a value, other
than ‘rsa’.
Upon successful return from the dkim_verify function, this
variable holds the value of the successfully verified DKIM header.
This value is unfolded and all whitespace is removed from it.
An example of using the ‘dkim_verify’ function:
require status
require dkim
prog eom
do
string result
switch dkim_verify(current_message())
do
case DKIM_VERIFY_OK:
set result "pass; verified for " .
dkim_verified_signature_tag('i')
case DKIM_VERIFY_PERMFAIL:
set result "fail (%dkim_explanation)"
case DKIM_VERIFY_TEMPFAIL:
set result "neutral"
done
header_add("X-Verification-Result", "dkim=%result")
done
The ‘dkim’ module defines convenience functions for manipulating with DKIM signatures:
Extracts the value of the tag tag from the DKIM signature sig. Signature must be normalized by performing the header unwrapping and removing whitespace characters.
If the tag was not found, returns empty string, unless tag is one of the tags listed in the table below. If any of these tags are absent, the following values are returned instead:
| Tag | Default value |
|---|---|
| c | ‘simple/simple’ |
| q | ‘dns/txt’ |
| i | ‘@’ + the value of the ‘d’ tag. |
Returns the value of tag tag from the ‘dkim_verified_signature’ variable.
This function is available only in the eom handler.
Signs the current message. Notice, that no other modification should be attempted on the message after calling this function. Doing so would make the signature invalid.
Mandatory arguments:
Name of the domain claiming responsibility for an introduction of a message into the mail stream. It is also known as the signing domain identifier (SDID).
The selector name. This value, along with d identifies the location of the DKIM public key necessary for verifying the message. The public key is stored in the DNS TXT record for
s._domainkey.d
Name of the disk file that keeps the private key for signing the message. The file must be in PEM format.
Optional arguments:
Canonicalization algorithm for message headers. Valid values are: ‘simple’ and ‘relaxed’. ‘simple’ is the default.
Canonicalization algorithm for message body. Valid and default values are the same as for ch.
A colon-separated list of header field names that identify the header fields that must be signed. Optional whitespace is allowed at either side of each colon separator. Header names are case-insensitive. This list must contain at least the ‘From’ header.
It may contain names of headers that are not present in the message being signed. This provides a way to explicitly assert the absence of a header field. For example, if headers contained ‘X-Mailer’ and that header is not present in the message being signed, but is added by a third party later, the signature verification will fail.
Similarly, listing a header field name once more than the actual number of its occurrences in a message allows you to prevent any further additions. For example, if there is a single ‘Comments’ header field at the time of signing, putting ‘Comments:Comments:’ in the headers parameter is sufficient to prevent any surplus ‘Comments’ headers from being added later on.
Multiple instances of the same header name are allowed. They mean that multiple occurrences of the corresponding header field will be included in the header hash. When such multiple header occurrences are referenced, they will be presented to the hashing algorithm in the reverse order. E.g. if the header list contained ‘Received:Received’) and the current message contained three ‘Received’ headers:
Received: A Received: B Received: C
then these headers will be signed in the following order:
Received: C Received: B
The default value for this parameter, split over multiple lines for readability, is as follows:
Signing algorithm: either ‘rsa-sha256’ or ‘rsa-sha1’. Default is ‘rsa-sha256’.
An example of using this function:
precious string domain "example.org"
precious string selector "s2048"
prog eom
do
dkim_sign("example.org", "s2048", "/etc/pem/my-private.pem",
"relaxed", "relaxed", "from:to:subject")
done
When sending a signed message, it is critical that no other
modifications be applied to the message after it has been signed.
Unfortunately, it is not always the case when mailfromd is
used with Sendmail. Before sending the message over SMTP,
Sendmail reformats the headers that contain a list of email
addresses, by applying to them a procedure called in its parlance
commaization. The following headers are modified:
Apparently-To, Bcc, Cc,
Disposition-Notification-To, Errors-To, From,
Reply-To, Resent-Bcc, Resent-Cc,
Resent-From, Resent-Reply-To, Resent-Sender,
Resent-To, Sender, To. Thus, if your
dkim_sign includes any of these in the signature (which is the
default) and some of them happen to be formatted other way than the
one Sendmail prefers, the DKIM signature would not verify on
the recipient side. To prevent this from happening, dkim_sign
mimics the Sendmail behavior and reformats those headers before
signing the message. This should ensure that the message signed and
the message actually sent are the same. This default behavior is
controlled by the following global variable:
“Commaize” the address headers (see the list above) of the message the same way Sendmail does, and then sign the resulting message.
The default value is 1 (true). You can set it to 0
(false) if this behavior is not what you want (e.g. if you are
using postfix or some other MTA).
The functions header_add and header_insert
(see Header modification functions) as well as the add
action (see header manipulation) cannot interact properly with
dkim_sign due to the shortcomings of the Milter API. If any of
these was called, dkim_sign will throw the e_badmmq
exception with the diagnostics following diagnostics:
MMQ incompatible with dkim_sign: op on h, value v
where op is the operation code (‘ADD HEADER’ or ‘INSERT HEADER’), h is the header name and v is its value.
The following example shows one graceful way of handling such exception:
prog eom
do
try
do
dkim_sign("example.org", "s2048", "/etc/pem/my-private.pem")
done
catch e_badmmq
do
# Purge the message modification queue
mmq_purge()
# and retry
dkim_sign("example.org", "s2048", "/etc/pem/my-private.pem")
done
done
See Message modification queue, for a discussion of the message modification queue.
Mailfromd Manual:
Follow these steps to set up your own DKIM record:
Use the openssl genrsa command. Run:
openssl genrsa -out private.pem 2048
The last argument is the size of the private key to generate in bits.
openssl rsa -in private.pem -pubout -outform PEM -out public.pem
A DKIM record is a TXT type DNS record that holds the public key part for verifying messages. Its format is defined in RFC 487125. The label for this record is composed as follows:
s._domainkey.d
where d is your domain name, and s is the selector you
chose to use. You will use these two values as parameters to the
dkim_sign function in your eom handler. E.g. if your
domain in ‘example.com’ and selector is ‘s2048’, then the
DKIM TXT record label is ‘s2048._domainkey.example.com’.
The public key file generated in step 2 will have the following contents:
-----BEGIN PUBLIC KEY----- base64 -----END PUBLIC KEY-----
where base64 is the key itself in base64 encoding. The minimal DKIM TXT record will be:
"v=DKIM1; p=base64"
The only mandatory tag is in fact ‘p=’. The use of ‘v=’ is recommended. More tags can be added as needed. In particular, while testing the DKIM support, it is advisable to add the ‘t=y’ tag.
Mailfromd Manual:
Socket map (sockmap for short) is a special type of database used in Sendmail and MeTA1. It uses a simple server/client protocol over INET or UNIX stream sockets. The server listens on a socket for queries. The client connects to the server and sends it a query, consisting of a map name and a key separated by a single space. Both map name and key are sequences of non-whitespace characters. The map name serves to identify the type of the query. The server replies with a response consisting of a status indicator and result, separated by a single space. The result part is optional.
For example, following is the query for key ‘smith’ in map ‘aliases’:
11:aliases news,
A possible reply is:
18:OK root@domain.net,
This reply means that the key ‘news’ was found in the map, and the value corresponding to that key is ‘root@domain.net’.
The following reply means the key was not found:
8:NOTFOUND,
For a detailed description of the sockmap protocol, see Protocol in Smap manual.
The MFL library provides two primitives for dealing with sockmaps. Both primitives become available after requiring the sockmap module.
This function look ups the key in the map. The fd
refers to the sockmap to use. It must be obtained as a result of a
previous call to open with the URL of the sockmap as
its first argument (see open). For example:
number fd open("@ unix:///var/spool/meta1/smap/socket")
string ret sockmap_query(fd, "aliases", $rcpt_to)
if ret matches "OK (.+)"
set alias \1
fi
close(fd)
This function connects to the sockmap identified by the url, queries for key in map and closes the connection. It is useful when you need to perform only a single lookup on the sockmap.
Mailfromd Manual:
The National Language Support functions allow you to write your scripts in such a way, that any textual messages they display are automatically translated to your native language, or, more precisely, to the language required by your current locale.
This section assumes the reader is familiar with the concepts of program
internationalization and localization. If not, please
refer to The Purpose of GNU
gettext in GNU gettext manual, before reading further.
In general, internationalization of any MFL script
follows the same rules as described in the GNU gettext manual.
First of all, you select the program message domain, i.e. the
identifier of a set of translatable messages your script contain.
This identifier is then used to select appropriate translation.
The message domain is set using textdomain function. For the
purposes of this section, let’s suppose the domain name is
‘myfilter’. All NLS functions are provided in the
nls module, which you need to require prior to using
any of them.
To find translations of textual message to the current locale, the
underlying gettext mechanism will look for file
dirname/locale/LC_MESSAGES/domainname.mo,
where dirname is the message catalog hierarchy name,
locale is the locale name, and domainname is the name of
the message domain. By default dirname is
/usr/local/share/locale, but you may change it using
bindtextdomain function. The right place for this initial
NLS setup is in the ‘begin’ block (see begin/end).
To summarize all the above, the usual NLS setup will look like:
require nls
begin
do
textdomain("myfilter")
bindtextdomain("myfilter", "/usr/share/locale");
done
For example, given the settings above, and supposing the environment
variable LC_ALL is set to ‘pl’, translations will be looked
in file /usr/share/locale/pl/LC_MESSAGES/myfilter.mo.
Once this preparatory work is done, you can request each message to
be translated by using gettext function, or _
(underscore) macro. For example, the following statement will produce
translated textual description for ‘450’ response:
tempfail 450 4.1.0 _("Try again later")
Of course it assumes that the appropriate myfile.mo file
already exists. If it does not, nothing bad happens: in this case the
macro _ (as well as gettext function) will simply
return its argument unchanged, so that the remote party will get the
textual message in English.
The ‘mo’ files are binary files created from ‘po’ source
files using msgfmt utility, as described in Producing Binary MO Files in GNU
gettext manual. In turn, the format of ‘po’ files is described
in The Format of PO Files in GNU gettext manual.
This function sets the base directory of the hierarchy containing message catalogs for a given message domain.
domain is a string identifying the textual domain. If it is not empty, the base directory for message catalogs belonging to domain domain is set to dirname. It is important that dirname be an absolute pathname; otherwise it cannot be guaranteed that the message catalogs will be found.
If domain is ‘""’, bindtextdomain returns the
previously set base directory for domain domain.
The rest of this section describes the NLS functions supplied in the nls module.
dgettext attempts to translate the string msgid into the
currently active locale, according to the settings of the textual
domain domain. If there is no translation available,
dgettext returns msgid unchanged.
The dngettext functions attempts to translate a text string
into the language specified by the current locale, by looking up the
appropriate singular or plural form of the translation in a message
catalog, set for the textual domain domain.
See Additional functions for plural forms in GNU gettext utilities, for a discussion of the plural form handling in different languages.
The textdomain function sets the current message domain to
domain, if it is not empty. In any case the function returns
the current message domain. The current domain is ‘mailfromd’
initially. For example, the following sequence of textdomain
invocations will yield:
textdomain("") ⇒ "mailfromd"
textdomain("myfilter") ⇒ "myfilter"
textdomain("") ⇒ "myfilter"
gettext attempts to translate the string msgid into the
currently active locale, according to the settings of the current textual
domain (set using textdomain function). If there is no
translation available, gettext returns msgid unchanged.
The ngettext functions attempts to translate a text string
into the language specified by the current locale, by looking up the
appropriate singular or plural form of the translation in a message
catalog, set for the current textual domain.
See Additional functions for plural forms in GNU gettext utilities, for a discussion of the plural form handling in different languages.
Mailfromd Manual:
The basic means for outputting diagnostic messages is the ‘echo’ instruction (see Echo), which sends its arguments to the currently established logging channel. In daemon mode, the latter is normally connected to syslog, so any echoed messages are sent there with the facility selected in mailfromd configuration and priority ‘info’.
If you want to send a message to another facility and/or priority, use the ‘syslog’ function:
Sends text to syslog. The priority argument is formed by ORing the facility and the level values (explained below). The facility level is optional. If not supplied, the currently selected logging facility is used.
The facility specifies what type of program is logging the message, and the level indicates its relative severity. The following symbolic facility values are declared in the syslog module: ‘LOG_KERN’, ‘LOG_USER’, ‘LOG_MAIL’, ‘LOG_DAEMON’, ‘LOG_AUTH’, ‘LOG_SYSLOG’, ‘LOG_LPR’, ‘LOG_NEWS’, ‘LOG_UUCP’, ‘LOG_CRON’, ‘LOG_AUTHPRIV’, ‘LOG_FTP’ and ‘LOG_LOCAL0’ through ‘LOG_LOCAL7’
The declared severity levels are: ‘LOG_EMERG’, ‘LOG_ALERT’, ‘LOG_CRIT’, ‘LOG_ERR’, ‘LOG_WARNING’, ‘LOG_NOTICE’, ‘LOG_INFO’ and ‘LOG_DEBUG’.
Mailfromd Manual:
These functions are designed for debugging the MFL programs.
Enable debugging. The value of spec sets the debugging level. See debugging level specification, for a description of its format.
For compatibility with previous versions, this function is also available under the name ‘mailutils_set_debug_level’.
This function returns the debugging level currently in effect for the source module srcname, or the global debugging level, if called without arguments.
For example, if the program was started with --debug='all.trace5;engine.trace8' option, then:
debug_level() ⇒ 127
debug_level("engine") ⇒ 1023
debug_level("db") ⇒ 0
Returns the current state of the callout SMTP transcript. The result is 1 if the transcript is enabled and 0 otherwise. The transcript is normally enabled either by the use of the --transcript command line option (see SMTP transcript) or via the ‘transcript’ configuration statement (see transcript).
The optional value, supplies the new state for SMTP transcript. Thus, calling ‘callout_transcript(0)’ disables the transcript.
This function can be used in bracket-like fashion to enable transcript for a certain part of MFL program, e.g.:
number xstate callout_transcript(1) on poll $f do … done set xstate callout_transcript(0)
Note, that the use of this function (as well as the use of the
--transcript option) makes sense only if callouts are
performed by the mailfromd daemon itself. It will not
work if a dedicated callout server is used for that purpose
(see calloutd).
Returns the current debugging level specification, as given by
--debug command line option or by the debug configuration
statement (see conf-debug).
If the argument srcnames is specified, it is treated as a semicolon-separated list of categories for which the debugging specification is to be returned.
For example, if mailfromd was started with
--debug=all.trace5;spf.trace1;engine.trace8;db.trace0, then:
debug_spec() ⇒ "all.trace5,engine.trace8"
debug_spec("all;engine") ⇒ "all.trace5,engine.trace8"
debug_spec("engine;db") ⇒ "db.trace0;engine.trace8"
debug_spec("prog") ⇒ ""
When called without arguments, debug_spec returns only
those categories which have been set, as shown in the first example
above.
Optional showunset parameters controls whether to return unset module specifications. To print all debugging specifications, whether set or not, use
debug_spec("", 1)
These three functions are intended to complement each other. The
calls to debug can be placed around some piece of code you wish
to debug, to enable specific debugging information for this code
fragment only. For example:
/* Save debugging level for dns.c source */ set dlev debug_spec("dns", 1) /* Set new debugging level */ debug("dns.trace8") . . . /* Restore previous level */ debug(dlev)
Enable tracing for a set of modules given in module argument. See --trace-program, for a description of its format.
Disable tracing for given modules.
This pair of functions is also designed to be used together in
a bracket-like fashion. They are useful for debugging
mailfromd, but are not advised to use otherwise, since
tracing slows down the execution considerably.
Generate a stack trace in this point. See tracing runtime errors, for the detailed description of stack traces.
The functions below are intended mainly for debugging MFL run-time
engine and for use in mailfromd testsuite. You will hardly
need to use them in your programs.
Expands the run-time data segment by at least n words.
Returns the value of the register r at the moment of the call. Symbolic names for run-time registers are provided in the module _register:
| Name | Register |
|---|---|
| REG_PC | Program counter |
| REG_TOS | Top of stack |
| REG_TOH | Top of heap |
| REG_BASE | Frame base |
| REG_REG | General-purpose accumulator |
| REG_MATCHSTR | Last matched string pointer |
Enters a time-consuming loop and waits there for n seconds (by
default – indefinitely). The intention is to facilitate attaching
to mailfromd with the debugger. Before entering the loop,
a diagnostic message is printed on the ‘crit’ facility, informing
about the PID of the process and suggesting the command to be used to
attach to it, e.g.:
mailfromd: process 21831 is waiting for debug mailfromd: to attach: gdb -ex 'set variable mu_wd::_count_down=0' /usr/sbib/mailfromd 21831
Mailfromd Manual:
MFL sources are usual ASCII files and you may
edit them with any editor you like. However, the best choice for this
job (as well as for many others) is, without doubt, GNU Emacs. To ease
the work of editing script files, the mailfromd package
provides a special Emacs mode, called MFL mode.
The elisp source file providing this mode, mfl-mode.el, is installed automatically, provided that GNU Emacs is present on your machine. To enable the mode, add the following lines to your Emacs setup file (either system-wide site-start.el, or your personal one, ~/.emacs):
(autoload 'mfl-mode "mfl-mode")
(setq auto-mode-alist (append auto-mode-alist
'(("/etc/mailfromd.mf" . mfl-mode)
("\\.mf$" . mfl-mode))))
The first directive loads the MFL mode, and the second one tells Emacs to apply it to any file whose name ends in /etc/mailfromd.mf26 or in a ‘.mf’ suffix.
MFL mode provides automatic indentation and syntax highlighting for MFL sources. The default indentation setup is the same as the one used throughout this book:
loop keyword.
(see mfl-loop-statement-offset). Continuation statements within
loop header are offset 5 columns from the indentation of their
controlling keyword, either for or while
(see mfl-loop-continuation-offset).
The mode provides two special commands that help navigate through the complex filter scripts:
Move to the beginning of current function or handler definition.
Move to the end of current function or handler definition.
Here, current function or handler means the one within which your cursor currently stays.
You can use C-M-e repeatedly to walk through all function and handler definitions in your script files. Similarly, repeatedly pressing C-M-a will visit all the definitions in the opposite direction (from the last up to the very first one).
Another special command, C-c C-c, allows to verify the
syntax of your script file. This command runs mailfromd in
syntax check mode (see Testing Filter Scripts) and displays its
output in a secondary window, which allows to navigate through
eventual diagnostic messages and to jump to source locations
described by them.
All MFL mode settings are customizable. To change any of them, press M-x customize and visit ‘Environment/Unix/Mfl’ customization group. This group offers two subgroups: ‘Mfl Lint group’ and ‘Mfl Indentation group’.
‘Mfl Lint group’ controls invocation of mailfromd by C-c C-c. This group contains two variables:
The mailfromd to be invoked. By default, it is
‘mailfromd’. You will have to change it, if mailfromd
cannot be found using PATH environment variable, or if you wish
to pass it some special options. However, do not include
--lint or -I options in this variable. The
--lint option is given automatically, and include paths are
controlled by mfl-include-path variable (see below).
A list of directories to be appended to mailfromd include
search path (see include search path). By default it is empty.
‘Mfl Indentation group’ controls automatic indentation of MFL scripts. This group contains the following settings:
This variable sets the basic indentation increment. It is set to 2, by default, which corresponds to the following indentation style:
prog envfrom
do
if $f = ""
accept
else
…
fi
done
Indentation offset for case and when lines, relative to
the column of their controlling keyword. The default is 0, i.e.:
switch x do case 0: … default: … done
Indentation offset of returns and alias statements,
relative to the controlling func keyword. The default value is
2, which corresponds to:
func foo() alias bar returns string
Indentation increment for multi-line comments. The default value is 1, which makes:
/* first comment line
second comment line */
Indentation increment for parts of a loop statement. The
default value is 5, which corresponds to the following style:
loop for stmt,
while cond,
incr
do
If any of the loop parts occupies several lines, the
indentation of continuation lines relative to the first line is
controlled by mfl-loop-continuation-offset, which defaults
to 5:
loop for set n 0
set z 1,
while n != 10
or z != 2,
set n n + 1
Mailfromd Manual:
mailfromdUpon startup, mailfromd checks if the file
/etc/mailfromd.conf exists.27 If it does, the program attempts to retrieve
its configuration settings from that file.
The mailfromd.conf file must be written in the GNU mailutils configuration format, as described in Configuration File Syntax in GNU Mailutils Manual. This format can be summarized as follows:
Inline comments begin with ‘//’ or ‘#’ and end at the end of the line. Multiline comments are delimited by ‘/*’ and ‘*/’. Multiline comments cannot be nested, but can contain inline comment markers.
Empty lines are ignored. Whitespace characters (i.e. horizontal, vertical space, and newline) are ignored, except as they serve to separate tokens.
A statement consists of a keyword and a value, separated by whitespace. Statements terminate with a semicolon. E.g.
pidfile /var/run/mailfromd.pid;
A block statement consists of a keyword and a list of statements enclosed in ‘{’ and ‘}’ characters. Optional label can appear between the keyword and opening curly brace. E.g.:
logging {
syslog on;
facility mail;
}
Block statement is not required to terminate with a semicolon, although it is allowed to.
The include statement causes
inclusion of the file listed as its value:
include /usr/share/mailfromd/config.inc;
The mailfromd.conf file is used by all programs that form the
‘mailfromd’ package, i.e. mailfromd,
calloutd, mfdbtool, and pmult. Since the sets
of statements understood by each of them differ, special syntactic means are
provided to separate program-specific configurations from each other.
First of all, if the argument to include is a directory, then
the program will search that directory for a file with the same name
as the base name of the program itself. If found, this file will be
loaded after finishing parsing the mailfromd.conf file.
Otherwise, this statement is ignored.
Secondly, the special block statement program tag is
processed only if tag matches the base name of the program being
run. Again, it is processed after the main mailfromd.conf
file.
Thus, if you need to provide configuration for the calloutd
component, there are two ways of doing so. First, you can place it to
a file named calloutd placed in a separate directory (say,
/etc/mailfromd.d), and use the name of that directory in a
include statement in the main configuration file:
include /etc/mailfromd.d;
Secondly, you can use the program statement as follows:
program calloutd {
...
}
Mailfromd Manual:
In addition to the usual data types (see Statements in GNU Mailutils Manual), mailfromd configuration
introduces the following two special ones:
The time interval specification is a string that defines an interval, much the same way we do this in English: it consists of one or more pairs ‘number’-‘time unit’. For example, the following are valid interval specifications:
1 hour 2 hours 35 seconds 1 year 7 months 2 weeks 2 days 11 hours 12 seconds
The pairs can occur in any order, however unusual it may sound to a human ear, e.g. ‘2 days 1 year’. If the ‘time unit’ is omitted, seconds are supposed.
A named pipe (socket).
An IPv4 connection to host address at port port. Port must be specified either as a decimal number or as a string representing the port name in /etc/services.
An IPv6 connection to host address at port port. This port type is not yet supported.
Mailfromd Manual:
Read filter script from file. By default it is read from sysconfdir/mailfromd.mf.
Initialize MFL variable name to value.
Add directories to the list of directories to be searched for header files. See include search path.
Argument is a list of directory names separated by colons.
Set program state directory. See statedir.
Append domain names from the named file to the list of relayed domains. This list can be inspected from MFL script using the ‘relayed’ function (see relayed).
The file argument is either a single file name or a list of file names, e.g.:
relayed-domain-file /etc/mail/sendmail.cw; relayed-domain-file (/etc/mail/sendmail.cw, /etc/mail/relay-domains);
Set source IP address for outgoing TCP connections.
Set the name of the file to store PID value in. The file must be
writable for the user or group mailfromd runs as
(see conf-priv).
Mailfromd Manual:
DNS resolver settings are configured using the resolver
compound statement:
resolver {
config filename;
max-cname-chain num;
}
Name of the resolver configuration file to use, instead of the default /etc/resolv.conf.
Maximum allowed length of a DNS CNAME chain that will be
followed. A CNAME chain is a sequence of CNAME records
pointing to another CNAMEs. Although CNAME chains are not
considered a good practice, many sites still use them. By default the
mailfromd resolver allows at most one CNAME record pointing
to a CNAME (this corresponds to max-cname-chain 2). If you
need to follow longer chains, raise this value. Note however, that
using values greater than 5 is not a good idea, anyway.
Mailfromd Manual:
A single mailfromd daemon can run several servers.
These are configured in the following statement:
server type {
id name;
listen url;
backlog num;
max-instances num;
single-process bool;
reuseaddr bool;
option list;
default bool;
callout url;
acl { … }
}
Define a server. The type is either ‘milter’ or ‘callout’. See SMTP Timeouts, for a description of various types of servers.
The substatements in the server block provide parameters for
configuring this server.
Assign an identifier to this server. This identifier is used as a suffix to syslog tag (see syslog tag) in messages related to this server. For example, if a server block had the following statement in it:
id main;
then all messages related to this server will be marked with tag ‘mailfromd#main’.
The part before the ‘#’ is set using the tag statement
in logging block (see Mailutils
Configuration File in GNU Mailutils Manual).
Listen for connections on the given URL. See milter port specification, for a description of allowed url formats.
Example:
listen inet://10.10.10.1:3331;
Configures the size of the queue of pending connections. Default value is 8.
Sets the maximum number of instances allowed for this server.
When set to ‘yes’, this server will run in single-process
mode, i.e. it will not fork sub-processes to serve requests. This
option is meant exclusively to assist in debugging
mailfromd. Don’t use it for anything else but for
debugging!
When set to ‘yes’, mailfromd will attempt to reuse
existing socket addresses. This is the default behavior.
If the server type is ‘callout’, the following statement is also allowed:
Configures server options. As of version 8.14 only one option is defined:
Mark this server as the default one. This means it will be used by
every milter server that doesn’t define the callout-url
statement.
When set to ‘yes’, this server is marked as a default callout server
for all milter servers declared in the configuration. This is
equivalent to option default.
if the server type is ‘milter’, you can use the following statement to query a remote callout server:
Use a callout server at url (see milter port specification).
You can also set a global callout server, which will be used
by all milter servers that do not set the callout statement:
Set global callout server. See milter port specification, for allowed url formats.
Mailfromd Manual:
Sets the timeout value for connection between the filter and the MTA. Default value is 7210 seconds. You normally do not need to change this value.
This block statement configures access control list for incoming Milter connections. See Mailutils Configuration File in GNU Mailutils Manual, for a description of its syntax. E.g.:
acl {
allow from 10.10.10.0/24;
deny from any;
}
Mailfromd Manual:
Set default logger mechanism. Allowed values for mech are:
Log everything to the standard error.
Log to syslog.
Log to syslog using the asynchronous syslog implementation.
See Logging and Debugging, for a detailed discussion. See also Using non-blocking syslog, for information on how to set default syslog implementation at compile time.
Set mailfromd debug verbosity level. The spec
must be a valid debugging level specification (see debugging level specification).
Enables stack trace dumps on runtime errors. This feature is useful for locating the source of an error, especially in complex scripts. See tracing runtime errors, for a detailed description.
Enable action tracing. If bool is ‘true’,
mailfromd will log all executed actions. See Logging and Debugging, for a detailed description of action tracing.
Enable program instruction tracing for modules in modlist, a comma-separated list of source code modules, e.g.:
trace-program (bi_io,bi_db);
This statement enables tracing for functions from modules bi_io.c and bi_db.c (notice, that you need not give file suffixes).
This tracing is useful for debugging mailfromd, but is not
advised to use otherwise, since it is very time-costly.
Enable transcripts of call-out SMTP sessions. See SMTP transcript, for a detailed description of SMTP transcripts.
Mailfromd Manual:
The SMTP timeouts used in callout sessions are configured via
smtp-timeout statement:
smtp-timeout type {
connection interval;
initial-response interval;
helo interval;
mail interval;
rcpt interval;
rset interval;
quit interval;
}
Declare SMTP timeouts of the given type, which may be ‘soft’ or ‘hard’.
Callout SMTP sessions initiated by polling functions, are controlled by two sets of timeouts: ‘soft’ and ‘hard’. Soft timeouts are used by the mailfromd milter servers. Hard timeouts are used by callout servers (see callout server). When a soft timeout is exceeded, the calling procedure is delivered an ‘e_temp_failure’ exception and the session is scheduled for processing by a callout server. The latter re-runs the session using hard timeouts. If a hard timeout is exceeded, the address is marked as ‘not_found’ and is stored in the cache database with that status.
Normally, soft timeouts are set to shorter values, suitable for use in MFL scripts without causing excessive delays. Hard timeouts are set to large values, as requested by RFC 2822 and guarantee obtaining a definite answer (see below for the default values).
The time argument for all smtp-timeout sub-statements
is expressed in time interval units, as described in time interval specification.
Sets initial connection timeout for callout tests. If the connection is not established within this time, the corresponding callout function returns temporary failure.
Sets the time to wait for the initial SMTP response.
Timeout for a response to ‘HELO’ (or ‘EHLO’) command.
Timeout for a response to ‘MAIL’ command.
Timeout for a response to ‘RCPT’ command.
Timeout for a response to ‘RSET’ command.
Timeout for a response to ‘QUIT’ command.
The default timeout settings are:
| Timeout | Soft | Hard |
|---|---|---|
| connection | 10s | 5m |
| initial-response | 30s | 5m |
| helo | I/O | 5m |
| I/O | 10m | |
| rcpt | I/O | 5m |
| rset | I/O | 5m |
| quit | I/O | 2m |
Table 7.1: Default SMTP timeouts
Sets a general SMTP I/O operation timeout. This timeout is used as the default for entries marked with ‘I/O’ in the above table. The default is 3 seconds.
Mailfromd Manual:
Sets default domain used in ‘EHLO’ (or ‘HELO’)
SMTP command when probing the remote host. This value can be
overridden by ‘from’ parameter to poll command
(see poll).
This statement assigns the value string to the ‘ehlo_domain’ variable (see ehlo_domain), and is therefore equivalent to
setvar ehlo_domain string;
Sets default email addresses used in ‘MAIL FROM:’
SMTP command when probing the remote host. This value can be
overridden by ‘as’ parameter to poll command
(see poll).
This statement assigns the value string to the ‘mailfrom_address’ variable (see mailfrom_address), and is therefore equivalent to
setvar mailfrom_address string;
Enables the use of SMTP VRFY statement prior to normal callout
sequence. If VRFY is supported by the remote server,
mailfromd relies on its reply and does not perform normal
callout.
The use of this statement is not recommended, because many existing VRFY implementations always return affirmative result, no matter is the requested email handled by the server or not.
The default is enable-vrfy no, i.e. VRFY is disabled.
Mailfromd Manual:
Switch to this user’s privileges after startup.
See Starting and Stopping, for a discussion of
the privileges mailfromd runs under and the options that
affect them. See also group below.
Retain the supplementary group name when switching to user
privileges. By default mailfromd clears the list of
supplementary groups when switching to user privileges, but this statement
allows to retain the given group. It can be specified multiple times
to retain several groups. This option may be necessary to
maintain proper access rights for various files. See Starting and Stopping.
Mailfromd Manual:
database dbname {
file name;
enable bool;
expire-interval interval;
positive-expire-interval interval;
negative-expire-interval interval;
}
The database statement controls run-time parameters of
a DBM database identified by dbname. Allowed
values for the latter are: ‘cache’, ‘rate’ and
‘greylist’ for main cache, DNS lookup, sending rate and
greylisting databases, correspondingly.
Set the database file name.
Enable or disable this database.
Set the expiration interval for this database dbname. See time interval specification, for a description of time format.
This statement is valid only for ‘cache’ database. It sets the expiration interval for positive (‘success’) cache entries.
This statement is valid only for ‘cache’ database, where it sets expiration interval for negative (‘not_found’) cache entries.
Set default database type. type is one of the database types supported by mailutils (i.e., for Mailutils 3.0: ‘gdbm’, ‘ndbm’, ‘bdb’, ‘kc’, and ‘tc’). Run
mailfromd --show-defaults | grep 'supported databases:'
to get a list of type names supported by your build of mailfromd.
Defines file mode for newly created database files. mode must be a valid file mode in octal.
Set maximum number of attempts to acquire the lock. The time
between each two successive attempts is given by
lock-retry-timeout statement (see below). After
the number of failed attempts, mailfromd gives up.
Set the time span between the two locking attempts. Any valid time interval specification (see time interval specification) is allowed as argument.
Mailfromd Manual:
The statements in the runtime section configure various values
used by MFL builtin functions.
Sets the maximum number of stream descriptors that can be opened simultaneously. Default is 1024. See I/O functions.
Sets the maximum number of available mailbox descriptors. This value is used by MFL mailbox functions (see Mailbox functions).
Sets the maximum number of messages that can be opened simultaneously
using the mailbox_get_message function. See Message functions, for details.
Mailfromd Manual:
The following standard Mailutils statements are understood:
| Statement | Reference |
|---|---|
| auth | See Mailutils Configuration File in GNU Mailutils Manual. |
| debug | See Mailutils Configuration File in GNU Mailutils Manual. |
| include | See Mailutils Configuration File in GNU Mailutils Manual. |
| logging | See Mailutils Configuration File in GNU Mailutils Manual. |
| mailer | See Mailutils Configuration File in GNU Mailutils Manual. |
| locking | See Mailutils Configuration File in GNU Mailutils Manual. |
Mailfromd Manual:
Mailfromd Command Line SyntaxThe mailfromd binary is started from the command line
using the following syntax (brackets indicate optional parts):
$ mailfromd [options] [asgn] [script]
The meaning of each invocation part is described in the table below:
The command line options (see options).
Sendmail macro assignments. These are currently meaningful only with the --test option (see test mode), but this may change in the future. Each assignment has the form:
var=value
where var is the name of a Sendmail macro and value is the value to be assigned to it.
The file name of the filter script, if other than the default one.
Mailfromd Manual:
Mailfromd Manual:
Run in daemon mode (default).
Load the script named in the command line and execute the function named start, or ‘main’, if start is not given. See Run Mode, for a detailed description of this feature.
Show compilation defaults. See Databases.
Run in test mode. See Testing Filter Scripts. Default state is ‘envfrom’. This option implies --stderr (see --stderr).
Mailfromd Manual:
Set socket for the default callout server. This is mainly useful together with the --mtasim option.
Stay in foreground. When given this option, mailfromd will
not disconnect itself from the controlling terminal and will run in
the foreground.
Retain the group name when switching to user privileges. See Starting and Stopping.
This option complements the group configuration statement
(see group).
Add the directory dir to the list of directories to be searched
for header files. This will affect the functioning of #include
statement. See include, for a discussion of file inclusion.
Set the URL of the mailer to use. See Mail Sending Functions.
This option is reserved for use by mtasim (see mtasim).
Set optimization level for code generator. Two levels are implemented: ‘0’, meaning no optimization, and ‘1’, meaning full optimization.
Set communication socket. Overrides the listen configuration
statement, which you are advised to use instead (see listen).
Set pidfile name. Overrides the pidfile configuration
statement, which you are advised to use instead (see pidfile).
Read relayed domains from file. Overrides the
relayed-domain-file configuration statement (see relayed-domain-file), which you are advised to use instead.
See Avoiding Verification Loops, and the description of
relayed function (see relayed) for more information.
Read resolver settings from file, instead of the default /etc/resolv.conf.
Set new program state directory. See Local state directory, for
the description of this directory and its purposes. This option
overrides the settings of state-directory configuration statement,
described in state-directory.
Set source address for TCP connections. Overrides the ‘source-ip’ configuration statement, which you are advised to use instead (see source-ip).
Switch to this user privileges after startup. Overrides the user
configuration file statement, which you are advised to use instead
(see user). Default user is ‘mail’.
Assign value to the global variable var. The variable must be declared in your startup script. See overriding initial values, for a detailed discussion of this option.
Mailfromd Manual:
Following command line options control the preprocessor feature. See Preprocessor, for a detailed discussion of these.
Do not run the preprocessor.
Use command as the external preprocessor instead of the default
m4.
Define a preprocessor symbol name to have a value value.
Undefine the preprocessor symbol name.
Stop after the preprocessing stage; do not run the compiler proper. The output is in the form of preprocessed source code, which is sent to the standard output.
Mailfromd Manual:
See time interval specification, for information on interval format.
Set MTA connection timeout. Overrides milter-timeout
statement in the mailfromd configuration file, which you are
advised to use instead (see milter-timeout).
Mailfromd Manual:
Mention column number in error messages. See location-column. Use --no-location-column to disable
Set debugging level. See Logging and Debugging.
Parse and compile the script file and dump the disassembled listing of the produced code to the terminal. See Logging and Debugging.
Enable debugging the script file parser. While parsing the file, the detailed dump of the parser states and tokens seen will be output.
Enable debugging the lexical analyzer. While parsing the script file, the detailed dump of the lexer states and matched rules will be output.
Show Sendmail macros used in the script file. The macro names are displayed as comma-separated lists, grouped by handler names. See Sendmail, for a detailed description of this option and its usage.
Parse and compile the script file and dump the parse tree in a printable form to the terminal.
Print a cross-reference of variables used in the filter script. See Testing Filter Scripts.
Stop after the preprocessing stage; do not run the compiler proper. The output is in the form of preprocessed source code, which is sent to the standard output. See Preprocessor.
Check script file syntax and exit. If the file is OK, return 0 to the shell, otherwise print appropriate messages to stderr and exit with code 78 (‘configuration error’).
Do not fork sub-processes to serve requests. This option is meant to
assist in debugging mailfromd. Don’t use it for anything
else but for debugging, as it terribly degrades performance!
Add MFL stack trace information to runtime error output.
Overrides stack-trace configuration statement. Use the
--no-stack-trace to disable trace information.
See tracing runtime errors, for more information on this feature.
Set desired logging level for gacopyz library
(see Gacopyz). There are five logging levels. The following
table lists them in order of decreasing priority:
Log fatal errors.
Log error messages.
Log warning messages.
Log informational messages. In particular, this enables printing messages on each subprocess startup and termination, which look like that:
Apr 28 09:00:11 host mailfromd[9411]: connect
from 192.168.10.1:50398
Apr 28 09:00:11 host mailfromd[9411]: finishing
connection
This level can be useful for debugging your scripts.
Log debugging information.
Log Milter protocol interactions. This level prints huge amounts of information, in particular it displays dumps of each Milter packet sent and received.
Although it is possible to set these levels independently of each
other, it is seldom practical. Therefore, the option
--gacopyz-log=level enables all logging levels from
level up. For example, --gacopyz-log=warn enables
log levels ‘warn’, ‘err’ and ‘fatal’. It is the
default. If you need to trace each subprocess startup and shutdown,
set --gacopyz-log=info. Setting the logging level to
‘proto’ can be needed only for Gacopyz developers, to
debug the protocol.
Set logger mechanism (mech is one of ‘stderr’, ‘syslog’, ‘syslog:async’). See Logging and Debugging.
Output logs to syslog facility.
Tag syslog entries with the given string, instead of the program name.
Include C source information in debugging messages. This is
similar to setting line-info yes in the debug
configuration block (see line-info in GNU Mailutils Manual).
The --no-source-info can be used to cancel the effect of the
line-info yes configuration statement.
You do not need this option, unless you are developing or debugging
mailfromd.
Synonym for --lint.
Enable or disable action tracing. If --trace is given,
mailfromd will log all executed actions. See Logging and Debugging.
Enable program instruction tracing. With this option
mailfromd will log execution of every instruction in the
compiled filter program. The optional arguments allows to specify a
comma-separated list of source code modules for which the tracing is
to be enabled, for example --trace-program=bi_io,bi_db enables
tracing for functions from modules bi_io.c and bi_db.c
(notice, that you need not give file suffixes in string).
This option is useful for debugging mailfromd, but is not
advised to use otherwise, since it is very time-costly.
Enable or disable transcript of the SMTP sessions to the log channel. See Logging and Debugging.
Selects default syslog mechanism for diagnostic output.
Directs all logging to standard output. Similar to --logger=stderr.
Same as --dump-xref. See Logging and Debugging.
Mailfromd Manual:
Give a short help summary.
Give a short usage message.
Print program version.
Mailfromd Manual:
Right after startup, when mailfromd has done the
operations that require root privileges, it switches to the privileges
of the user it is configured to run as (see default user privileges) or
the one given in its configuration file (see user). During
this process it will drop all supplementary groups and switch to the
principal group of that user.
Such limited privileges of the daemon can cause difficulties if your
filter script needs to access some files (e.g. Sendmail
databases) that are not accessible to that user and group. For
example, the following fragment using dbmap function:
if dbmap("/etc/mail/aliases.db", $f, 1)
…
fi
will normally fail, because /etc/mail/aliases.db is readable only to the root and members of the group ‘smmsp’.
In such situations you need to instruct mailfromd to
retain the privileges of one or several supplementary groups when
switching to the user privileges. This is done using group
statement in the mailfromd configuration file
(see group). In example above, you need to use the following
settings:
group smmsp;
(The same effect can be achieved with --group command line option: mailfromd --group=smmsp).
To stop a running instance of mailfromd use one of the
following signals: SIGQUIT, SIGTERM, SIGINT.
All three signals have the same effect: the program cancels handling any
pending requests, uninitializes the communication socket (if it is a
UNIX socket, the program unlinks it) and exits.
To restart the running mailfromd instance, send it
SIGHUP. For restart to be possible, two conditions must be
met: mailfromd must be invoked with the full file name, and the
configuration file name must be full as well. If either of them is not
met, mailfromd displays a similar warning message:
warning: script file is given without full file name warning: restart (SIGHUP) will not work
or:
warning: mailfromd started without full file name warning: restart (SIGHUP) will not work
The reaction of mailfromd on SIGHUP in this case is
the same as on the three signals described previously, i.e. cleanup
and exit immediately.
The PID of the master instance of mailfromd is
kept on the pidfile, which is named mailfromd.pid and is
located in the program state directory. Assuming the default
location of the latter, the following command will stop the running
instance of the daemon:
kill -TERM `head -n1 /usr/local/var/mailfromd/mailfromd.pid`
The default pidfile location is shown in the output of mailfromd
--show-defaults (see Databases), and can be changed at run time using
pidfile statement (see pidfile).
To facilitate the use of mailfromd, it is shipped with a shell
script that can be used to launch it on system startup and shut it
down when the system goes down. The script, called
rc.mailfromd, is located in the directory /etc of the
distribution. It takes a single argument, specifying the action that
should be taken:
Start the program.
Shut down the program
Reload the program, by sending it SIGHUP signal.
Shut down the program and start it again.
Display program status. It displays the PID of the master process and its command line, for example:
$ /etc/rc.d/rc.mailfromd status mailformd appears to be running at 26030 26030 /usr/local/sbin/mailfromd --group smmsp
If the second line is not displayed, this most probably mean that there is a ‘stale’ pidfile, i.e. the one left though the program is not running.
An empty rc.mailfromd status output means that
mailfromd is not running.
Check the script file syntax, report any errors found and exit. If file is given it is checked instead of the default one.
Parse the script file (or file, if it is given, extract the names of Sendmail macros it uses and generate corresponding export statements usable in the Sendmail configuration file. By default, mc statements are generated. If -c (--cf) is given, the statements for sendmail.cf are output. See the next chapter for the detailed description of this mode.
You can pass any additional arguments to mailfromd by
editing ARGS variable near line 22.
The script is not installed by default. You will have to copy it to the directory where your system start-up scripts reside and ensure it is called during the system startup and shut down. The exact instructions on how to do so depend on the operating system you use and are beyond the scope of this manual.
Mailfromd Manual:
mailfromd with Various MTAsThe following sections describe how to configure various Milter-capable
MTAs to work with mailfromd.
Mailfromd Manual:
mailfromd with Sendmail.This chapter assumes you are familiar with Sendmail configuration in
general and with Milter configuration directives in particular. It
concentrates only on issues, specific for mailfromd.
To prepare Sendmail to communicate with
mailfromd you need first to set up the milter port.
This is done with INPUT_MAIL_FILTER statement in your
Sendmail file:
INPUT_MAIL_FILTER(`mailfrom', `S=unix:/usr/local/var/mailfromd/mailfrom')
Make sure that the value of ‘S’ matches the value of
listen statement in your mailfromd.conf file
(see listen). Notice, however, that they
may not be literally the same, because listen allows to
specify socket address in various formats, whereas Sendmail’s ‘S’
accepts only milter format.
If you prefer to fiddle directly with sendmail.cf file, use this statement instead:
Xmailfrom, S=unix:/usr/local/var/mailfromd/mailfrom
If you are using Sendmail version 8.14.0 or newer, you may skip to
the end of this section. These versions implement newer Milter
protocol that enables mailfromd to negotiate with the
MTA the macros it needs for each state.
Older versions of Sendmail do not offer this feature. For Sendmail
versions prior to 8.14.0, you need to manually configure
Sendmail to export macros you need in your
mailfromd.mf file. The simplest way to do so is using
rc.mailfromd script, introduced in the previous chapter.
Run it with macros command line argument and copy its output to
your sendmail.mc configuration file:
$ rc.mailfromd macros
If you prefer to work with sendmail.cf directly, use -c (--cf) command line option:
$ rc.mailfromd macros -c
Finally, if you use other mailfromd script file than that already installed (for example, you are preparing a new configuration while the old one is still being used in production environment), give its name in the command line:
$ rc.mailfromd macros newscript.mf
# or:
$ rc.mailfromd macros -c newscript.mf
If you use this method, you can skip the rest of this chapter. However, if you are a daring sort of person and prefer to do everything manually, follow the instructions below.
First of all you need to build a list of macros used by handlers in
your mailfromd.mf file. You can obtain it running
mailfromd --dump-macros. This will display all macros used
in your handlers, grouped by handler name, for example:
envfrom i, f, {client_addr}
envrcpt f, {client_addr}, {rcpt_addr}
Now, modify confMILTER_MACROS_handler macros in your
mc file. Here, handler means the uppercase name of the
mailfromd handler you want to export macros to, i.e. the
first word on each line of the above mailfromd --dump-macros
output. Notice, that in addition to these macros, you should
also export the macro i for the very first handler
(rc.mailfromd macros takes care of it automatically, but you
preferred to do everything yourself...) It is necessary in
order for mailfromd to include ‘Message-ID’ in its log
messages (see Message-ID).
For example, given the above macros listing, which corresponds to our sample configuration (see Filter Script Example), the sendmail.mc snippet will contain:
define(`confMILTER_MACROS_ENVFROM',dnl
confMILTER_MACROS_ENVFROM `, i, f, {client_addr}')
define(`confMILTER_MACROS_ENVRCPT',dnl
confMILTER_MACROS_ENVRCPT `, f, {client_addr}, {rcpt_addr}')
Special attention should be paid to s macro
(‘HELO’ domain name). In Sendmail versions up to
8.13.7 (at least) it is available only to helo handler. If you
wish to make it available elsewhere you will need to use the method
described in HELO Domain
Now, if you are a really daring person and prefer to do everything manually and to hack your sendmail.cf file directly, you certainly don’t need any advices. Nonetheless, here’s how the two statements above could look in this case:
O Milter.macros.envfrom=i, {auth_type}, {auth_authen}, \
{auth_ssf}, {auth_author}, {mail_mailer}, {mail_host}, \
{mail_addr} ,{mail_addr}, {client_addr}, f
O Milter.macros.envrcpt={rcpt_mailer}, {rcpt_host}, \
{rcpt_addr} ,i, f, {client_addr}
Mailfromd Manual:
mailfromd with MeTA1.MeTA1 (http://www.meta1.org) is an MTA of next generation which is designed to provide the following main features:
Instead of using Sendmail-compatible Milter protocol,
it implements a new protocol, called policy milter, therefore an
additional program is required to communicate with
mailfromd. This program is a Pmilter–Milter
multiplexer pmult, which is part of the ‘Mailfromd’
distribution. See pmult, for a detailed description of its configuration.
The configuration of ‘Meta1--Mailfromf’ interaction can be subdivided into three tasks.
mailfromd
This was already covered in previous chapters. No special ‘MeTA1’-dependent configuration is needed.
pmult to communicate with mailfromd
This is described in detail in pmult.
pmult
The MeTA1 configuration file is located in /etc/meta1/meta1.conf.
Configure the smtps component, by adding the following
section:
policy_milter {
socket {
type = type;
address = addr;
[path = path;]
[port = port-no;]
};
[timeout = interval;]
[flags = { flag };]
};
Statements in square brackets are optional. The meaning of each instruction is as follows:
type = typeSet the type of the socket to communicate with pmult.
Allowed values for type are:
Use INET socket. The socket address and port number are
set using the address and port statements (see below).
Use UNIX socket. The socket path is given by the
path statement (see below).
Notice, that depending on the type setting you have to set up
either address/port or path, but not both.
address = addrConfigure the socket address for type = inet. Addr is
the IP address on which pmult is listening
(see listen statement).
port = port-noPort number pmult is listening on
(see listen statement).
path = socket-fileFull pathname of the socket file, if type = unix.
timeout = intervalSets the maximum amount of time to wait for a reply from
pmult.
The behavior of smtps in case of time out depends
on the flags settings:
flags = { flag }Flag is one of the following:
If pmult does not respond, abort the current SMTP
session with a ‘421’ error.
If pmult does not respond, continue the current session
but try to reconnect for the next session.
For example, if the pmult configuration has:
listen inet://127.0.0.1:3333;
then the corresponding part in /etc/meta1/meta1.conf will be
smtps {
policy_milter {
socket {
type = inet;
address = 127.0.0.1;
port = 3333;
};
…
};
…
};
Similarly, if the pmult configuration has:
listen unix:///var/spool/meta1/pmult/socket;
then the /etc/meta1/meta1.conf should have:
smtps {
policy_milter {
socket {
type = unix;
path = /var/spool/meta1/pmult/socket;
};
…
};
…
};
Mailfromd Manual:
mailfromd with PostfixTo configure postfix to work with your filter, you
need to inform it about the socket your filter is listening on.
The smtpd_milters (or non_smtpd_milters) statement in
/etc/postfix/main.cf serves this purpose. If the filter is
to handle mail that arrives via SMTP, use
smtpd_milters. If it is to handle mail submitted locally to the
queue, use non_smtpd_milters. In both cases, the value
is a whitespace-separated list of socket addresses. Note, that Postfix
syntax for socket addresses differs from that used by Sendmail and
mailfromd. The differences are summarized in the following table:
| Sendmail | Mailfromd | Postfix |
|---|---|---|
| inet:port@host | inet://host:port | inet:host:port |
| unix:file | unix://file | unix:file |
Table 9.1: Socket addresses in various formats
For example, if your mailfromd listens on
‘inet://127.0.0.1:4111’, add the following to
/etc/postfix/main.cf:
smtpd_milters = inet:127.0.0.1:4111
Mailfromd uses Milter protocol version 6. Postfix, starting from
version 2.6 uses the same version. Older versions of Postfix use
Milter protocol 2 by default. Normally, it should not be a problem,
as mailfromd tries to detect what version the server is
speaking. If, however, it fails to select the proper version, you
will have to instruct Postfix what version to use. To do so, add the
following statement to /etc/postfix/main.cf:
milter_protocol = 6
The way Postfix handles macros differs from that of Sendmail.
Postfix emulates a limited subset of Sendmail macros, and not
all of them are are available when you would expect them to. In
particular, the ‘i’ macro is not available before the ‘DATA’
stage, which brings two consequences. First, mailfromd log
messages will not include message ID until the ‘DATA’ stage is
reached. Secondly, you cannot use ‘i’ in handlers ‘connect’,
‘helo’, ‘envfrom’ and ‘envrcpt’,
If you wish to tailor Postfix defaults to export the actual macros
used by your filter, run mailfromd --dump-macros and filter
its output through the postfix-macros.sed filter, which is
installed to the prefix/share/mailfromd directory,
e.g.:
$ mailfromd --dump-macros | \
sed -f /usr/share/mailfromd/postfix-macros.sed
milter_helo_macros = {s}
milter_mail_macros = {client_addr} {s} {f}
milter_rcpt_macros = {rcpt_addr} {f} {client_addr}
milter_end_of_data_macros = {i}
Cut and paste its output to your /etc/postfix/main.cf.
For more details regarding Postfix interaction with Milter and available Postfix configuration options, see Postfix before-queue Milter support.
Mailfromd Manual:
calloutdThe callout verification is usually performed by a special instance of
mailfromd (see callout server). However, it is also
possible to set up a dedicated callout server on a separate machine.
You can choose to do so, for instance, in order to reduce the load on
the server running mailfromd.
This stand-alone callout facility is provided by the
calloutd daemon.
Mailfromd Manual:
Main configuration file /etc/mailfromd.conf is used
(see Mailfromd Configuration). The configuration statements are
basically the same as for mailfromd.
The address to listen on is defined in the server statement.
Basically, it is the only statement the configuration file is required
to have. The minimal configuration can look like:
program calloutd {
server {
listen inet://198.51.100.1:3535;
}
}
To instruct the mailfromd daemon to use this server, the
following statement should be added to the /etc/mailfromd.conf
file:
program mailfromd {
callout-url inet://198.51.100.1:3535;
}
The server statement differs a little from the similar
statement for mailfromd. This and another
calloutd-specific statements are described in detail in the
subsections that follow. The rest of statements is shared with
mailfromd. The following table lists all supported
configuration statements along with cross-references to the
correspondent descriptions:
| Statement | Reference |
|---|---|
acl | See Mailutils Configuration File in GNU Mailutils Manual. |
auth | See Mailutils Configuration File in GNU Mailutils Manual. |
database | See conf-database. |
database-mode | See database-mode. |
database-type | See database-type. |
debug (section) | See Mailutils Configuration File in GNU Mailutils Manual. |
debug | See conf-calloutd-log. |
ehlo-domain | See ehlo-domain. |
enable-vrfy | See enable-vrfy. |
group | See group. |
include | See Mailutils Configuration File in GNU Mailutils Manual. |
io-timeout | See io-timeout. |
locking | See Mailutils Configuration File in GNU Mailutils Manual. |
lock-retry-count | See lock-retry-count. |
lock-retry-timeout | See lock-retry-timeout. |
logger | See conf-calloutd-log. |
logging | See Mailutils Configuration File in GNU Mailutils Manual. |
mailer | See Mailutils Configuration File in GNU Mailutils Manual. |
mail-from-address | See mail-from-address. |
pidfile | See pidfile. |
server | See conf-calloutd-server. |
source-ip | See source-ip. |
smtp-timeout | See conf-timeout. |
state-directory | See state-directory. |
transcript | See conf-calloutd-log, |
user | See user. |
Mailfromd Manual:
calloutd General SetupSets source IP address for TCP connections.
Defines the name of the file to store PID value in.
Sets the name of the program state directory. See statedir.
Mailfromd Manual:
server statementThe server statement configures how calloutd will
communicate with the client mailfromd server.
server {
id name;
listen url;
backlog num;
max-instances num;
single-process bool;
reuseaddr bool;
default bool;
callout url;
acl { … }
}
Define a server. Optional label may follow the server
keyword. The label is ignored.
The substatements in the server block provide parameters for
configuring this server.
Assign an identifier to this server. This identifier is used as a suffix to syslog tag (see syslog tag) in messages related to this server. For example, if a server block had the following statement in it:
id main;
then all messages related to this server will be marked with tag ‘calloutd#main’.
The part before the ‘#’ is set using the tag statement
in logging block (see Mailutils
Configuration File in GNU Mailutils Manual).
Listen for connections on the given URL. See milter port specification, for a description of allowed url formats.
Example:
listen inet://10.10.10.1:3331;
Configures the size of the queue of pending connections. Default value is 8.
Sets the maximum number of instances allowed for this server.
When set to ‘yes’, this server will run in single-process
mode, i.e. it will not fork sub-processes to serve requests. This
option is meant exclusively to assist in debugging
calloutd. Don’t use it for anything else but for
debugging!
When set to ‘yes’, calloutd will attempt to reuse
existing socket addresses. This is the default behavior.
Defines access control list for this server. See Mailutils Configuration File in GNU Mailutils Manual, for a detailed discussion.
If the global ACL is defined as well, an incoming connection is checked against both lists: first the per-server ACL, then the global one. The connection will be permitted only if it passes both checks.
Mailfromd Manual:
calloutd loggingSet default logger mechanism. Allowed values for mech are:
Log everything to the standard error.
Log to syslog.
Log to syslog using the asynchronous syslog implementation.
See Logging and Debugging, for a detailed discussion. See also Using non-blocking syslog, for information on how to set default syslog implementation at compile time.
Set mailfromd debug verbosity level. The spec
must be a valid debugging level specification (see debugging level specification).
If the boolean value bool is ‘true’, enables the transcript of call-out SMTP sessions.
Mailfromd Manual:
The calloutd invocation syntax is:
calloutd [option...]
The following options are available:
Stay in foreground. When given this option, calloutd will
not disconnect itself from the controlling terminal and will run in
the foreground.
Retain the group name when switching to user privileges. See Starting and Stopping.
Set pidfile name. Overrides the pidfile configuration
statement, which you are advised to use instead (see pidfile).
Read resolver settings from file, instead of the default /etc/resolv.conf.
Set source address for TCP connections. Overrides the ‘source-ip’ configuration statement, which you are advised to use instead (see source-ip).
Do not fork sub-processes to serve requests. This option is meant to
assist in debugging calloutd. Don’t use it for anything
else but for debugging, as it terribly degrades performance!
Set new program state directory. See Local state directory, for the description of this directory and its purposes.
Switch to this user’s privileges after startup. Overrides the user
configuration file statement, which you are advised to use instead
(see user). Default user is
‘mail’.
Set debugging level. See Logging and Debugging.
Output logs to syslog facility.
Tag syslog entries with the given string, instead of the program name.
Set logger mechanism (mech is one of ‘stderr’, ‘syslog’, ‘syslog:async’). See Logging and Debugging.
Selects default syslog mechanism for diagnostic output.
Directs all logging to standard output. Similar to --logger=stderr.
Set source address for TCP connections. Overrides the ‘source-ip’ configuration statement, which you are advised to use instead (see source-ip).
Set Mailutils debugging level. See http://mailutils.org/wiki/Debug_level, for a detailed discussion of level argument.
Include C source information in debugging messages. This is
similar to setting line-info yes in the debug
configuration block (see line-info in GNU Mailutils Manual).
The --no-source-info can be used to cancel the effect of the
line-info yes configuration statement.
You do not need this option, unless you are developing or debugging
calloutd.
Enable or disable transcript of the SMTP sessions to the log channel. See Logging and Debugging.
Load this configuration file.
Check syntax of configuration files and exit. Exit code is 0 if the file or files are OK, and 78 otherwise.
Verbosely log parsing of the configuration files.
Don’t load site-wide configuration file.
Set configuration parameter
Show configuration file summary.
Show compilation options.
Give a short help list.
Give a short usage message.
Print program version
Mailfromd Manual:
This section describes the protocol used to communicate with the
calloutd server.
The protocol works over stream-oriented TCP/IP transport. Either UNIX or IPv4 socket can be used. Commands and responses are terminated by a single CR LF pair. Each command occupies exactly one line. If the server succeeded in executing the command, it replies with a line starting with the word ‘OK’. Depending on the command, this keyword may be followed by a single space character and additional information. More information can be returned in unsolicited replies before the ‘OK’ line. Each unsolicited reply line starts with and asterisk followed by a single horizontal space character.
On error, the server replies with ‘NO’ followed by a horizontal space character and human-readable description of the problem.
The valid commands are discussed below. In examples illustrating the commands, the lines sent by the client are prefixed with C:, and lines sent by the server are prefixed with S:.
Adds email to the queue of email addresses to be verified. Available options are:
Sets verification mode for this email address. Available modes are:
The default mode.
If the host option is also given, its argument is taken as
the domain name. Otherwise, domain part of email is used.
The verification goes as follows. First, determine MX servers for that domain. Query each of them in order of increasing priority. First of them that replies determines the result of the test.
If no MX servers are defined for that domain, look for its ‘A’ record. If available, run SMTP probe on that IP.
Query MX servers for the domain specified with the host option.
Query the server whose name or IP address is supplied with the
host option.
The reverse of mxfirst: first query the host, then the MX
servers. The domain must be specified using the host option.
Supplies the domain name for mxonly and mode, and host name or
IP address for hostfirst and hostonly modes. The use of
this keyword with any of these modes is mandatory.
Use string as the argument to the SMTP EHLO command.
Use email in the SMTP MAIL FROM command.
On success, the server replies with ‘OK’, followed by a non-negative session ID for that email:
C: VRFY gray@example.org S: OK 0000000001
Query value of internal callout parameters. Valid values for arg are:
Return the string used as argument to the SMTP EHLO command.
Return the email address that is used in the SMTP MAIL FROM command.
On success, the server returns the requested value (if found) in an unsolicited reply:
C: GET ehlo timeout S: * ehlo=example.net S: OK
Sets string as session identifier for that session. Example:
C: SID deadbeef S: OK
Sets timeouts for various stages of SMTP session. On success, ‘OK’ is returned.
C: timeout 300 300 300 600 300 300 120 S: OK timeouts set
Runs callout session for emails registered with the vrfy
command. On success, results of the check are returned after the
‘OK’ keyword in a whitespace-separated list of
‘id=result’ pairs. In each pair, id is its
identifier as returned in the reply to the VRFY command and
result is one of the following result strings: ‘success’,
‘not_found’, ‘failure’, ‘temp_failure’, ‘timeout’.
Additional information about each callout session is returned in unsolicited replies. Each such reply is prefixed with the email identifier and callout stage name. Stage names are:
INIT remote_nameThe calloutd server is establishing communication with the
remote SMTP server remote_name.
GRTNG linecalloutd received initial response from the remote server.
line is the first line of the reply.
HELO linecalloutd received response to the EHLO (or
HELO) command. In case of multiline response, line is
the first line.
SENT commandThe SMTP command command has been sent to the remote server.
RECV lineThe remote server returned line in response. In case of multiline response, line is the first line.
Example of verification session:
C: RUN S: * 0000000000 INIT mx.example.org S: * 0000000000 GRTNG 220 mx.example.org ESMTP Ready S: * 0000000000 HELO 250-mx.example.org Hello tester S: * 0000000000 SENT RCPT TO:<gray@example.org> S: * 0000000000 RECV 250 Accepted S: * 0000000001 INIT foo.example.net S: * 0000000001 GRTNG 220 foo ESMTP server ready S: * 0000000001 HELO 250-foo.example.net Hello S: * 0000000001 SENT RCPT TO:<gray@example.net> S: * 0000000001 RECV 450 4.7.0 You are greylisted for 3600 seconds OK 0000000000=success 0000000001=temp_failure
Drop the email with the given serial number from the verification queue. Example:
C: DROP 0000000002 S: OK
Finishes the current session and disconnects from the callout server.
C: QUIT S: OK bye
Mailfromd Manual:
mfdbtoolThe mfdbtool utility manages mailfromd databases.
Mailfromd Manual:
mfdbtoolThe following options request the operation to be performed on the database. Exactly one of them must be specified. Each of them implied the --stderr option (see --stderr).
List the database. By default, ‘cache’ database is assumed. To list another database, use --format option (see --format).
Delete given entries from the database (see deleting from databases). By default, ‘cache’ database is assumed. To specify another database, use --format option (see --format).
Delete all expired entries from the database (see Database Maintenance). By default, ‘cache’ database is assumed. To specify another database, use --format option (see --format). Full database name can be given in the command line (see --file option below), if it differs from the one specified in the script file.
Use with the option --all (see --all) to expire all databases.
See Database Maintenance.
Compact database (see compaction). By default, ‘cache’ database is compacted. To specify another database, use --format option (see --format). Full database name can be given in the command line (see --file option below), if it differs from the one specified in the script file.
Use with the option --all (see --all) to compact all databases.
See compaction.
The following options modify the behavior of mfdbtool:
When used with --compact or --expire option, applies the action to all available databases. See compact cronjob.
Sets debugging level. The string argument must be a valid mailfromd debug level specification, as described in debugging level specification.
Set expiration intervals for all databases to the specified interval.
See time interval specification, for a description of
interval format. The option overrides the
expire-interval configuration statement
(see expire-interval-conf), which you are advised to use instead.
Set the name of the database to operate upon (for --compact,
--delete, --expire, and --list options).
Useful if, for some reason, you need to operate on a database whose
file name does not match the one mfdbtool is configured to
use.
Use database of the given format, instead of the default ‘cache’. See Basic Database Operations.
Ignore records that cannot be retrieved while compacting the
database. Without this option, mfdbtool will abort the
compaction if any such error is encountered.
Used with --list enables printing of the estimated times of sending along with the ‘rate’ database dump. Implies --list --format=rate. See estimated time of sending.
Sets program state directory. See Local state directory, for
the description of this directory and its purposes. This option
overrides the state-directory configuration statement,
described in state-directory.
Set format to be used for timestamps in listings, produced by
--list. The format is any valid strftime format
string, see Time and Date Formats, for a detailed description.
The default format is ‘%c’ (see %c time format). To
analyze mfdbtool --list output using text tools, such as
awk or grep, the following format might be useful:
‘%s’ (see %s time format). Another format I find useful is
‘%Y-%m-%d_%H:%M:%S’.
Mailfromd Manual:
mfdbtoolConfiguration settings are read from the /etc/mailfromd.conf file (see Mailfromd Configuration). The following statements are understood:
| Statement | Reference |
|---|---|
database | See conf-database. |
database-mode | See database-mode. |
database-type | See database-type. |
debug | See conf-calloutd-log. |
lock-retry-count | See lock-retry-count. |
lock-retry-timeout | See lock-retry-timeout. |
state-directory | See state-directory. |
Mailfromd Manual:
mtasim — a testing toolThe mtasim utility is a MTA simulator for testing
mailfromd filter scripts. By default it operates in
stdio mode, similar to that of sendmail -bs. In this
mode it reads SMTP commands from standard input and sends
its responses to the standard output. There is also another mode,
called daemon, where mtasim opens a TCP
socket and listens on it much like any MTA does. In both
modes no actual delivery is performed, the tool only simulates the
actions an MTA would do and responses it would give.
This tool is derived from the program mta, which I wrote
for GNU Anubis test suite.
Mailfromd Manual:
mtasim interactive mode modeIf you start mtasim without options, you will see the
following:
220 mtasim (mailfromd 8.14) ready (mtasim) _
The first line is an usual RFC 2821 reply. The second one is
a prompt, indicating that mtasim is in interactive mode and
ready for input. The prompt appears only if the package is compiled
with GNU Readline and mtasim determines that its standard
input is connected to the terminal. This is called interactive
mode and is intended to save the human user some typing by offering
line editing and history facilities (see Command Line Editing in GNU Readline Library). If the package
is compiled without GNU Readline, you will see:
220 mtasim (mailfromd 8.14) ready _
where ‘_’ represents the cursor. Whatever the mode,
mtasim will wait for further input.
The input is expected to consist of valid SMTP commands
and special mtasim statements. The utility will act exactly
like a RFC 2821-compliant MTA, except that it will
not do actual message delivery or relaying. Try typing HELP to
get the list of supported commands. You will see something similar
to:
250-mtasim (mailfromd 8.14); supported SMTP commands: 250- EHLO 250- HELO 250- MAIL 250- RCPT 250- DATA 250- HELP 250- QUIT 250- HELP 250 RSET
You can try a simple SMTP session now:
220 mtasim (mailfromd 8.14) ready (mtasim) ehlo localhost 250-pleased to meet you 250 HELP (mtasim) mail from: <me@localhost> 250 Sender OK (mtasim) rcpt to: <him@domain> 250 Recipient OK (mtasim) data 354 Enter mail, end with `.' on a line by itself (mtasim) . 250 Mail accepted for delivery (mtasim) quit 221 Done
Notice, that mtasim does no domain checking, so such thing
as ‘rcpt to: <him@domain>’ was eaten without complaints.
So far so good, but what all this has to do with
mailfromd? Well, that’s what we are going to explain. To
make mtasim consult any milter, use --port
(-X) command line option. This option takes a single
argument that specifies the milter port to use. The port can be given
either in the usual Milter format (See milter port specification,
for a short description), or as a full sendmail.cf style
X command, in which case it allows to set timeouts as well:
$ mtasim --port=inet:999@localhost
# This is also valid:
$ mtasim --port='mailfrom, S=inet:999@localhost, F=T, T=C:100m;R:180s'
If the milter is actually listening on this port, mtasim
will connect to it and you will get the following initial prompt:
220-mtasim (mailfromd 8.14) ready 220 Connected to milter inet://localhost:999 (mtasim)
Notice, that it makes no difference what implementation is listening
on that port, it may well be some other filter, not necessarily
mailfromd.
However, let’s return to mailfromd. If you do not want to
connect to an existing mailfromd instance, but prefer
instead to create a new one and run your tests with it (a preferred
way, if you already have a stable filter running but wish to test a
new script without disturbing it), use --port=auto. This
option instructs mtasim to do the following:
mailfromd. The arguments and
options for that instance may be given in the invocation of
mtasim after a double-dash marker (‘--’)
When mtasim exits, it terminates the subsidiary
mailfromd process and removes the temporary directory it has
created. For example, the following command will start
mailfromd -I. -I../mflib test.rc:
$ mtasim -Xauto -- -I. -I../mflib test.rc 220-mtasim (mailfromd 8.14) ready 220 Connected to milter unix:/tmp/mtasim-j6tRLC/socket (mtasim)
The /tmp/mtasim-j6tRLC directory and any files within it will
exist as long as mtasim is running and will be removed when
you exit from it.28 You can also instruct the subsidiary
mailfromd to use this directory as its state directory
(see statedir). This is done by --statedir command line
option:
$ mtasim -Xauto --statedir -- -I. -I../mflib test.rc
(notice that --statedir is the mtasim option,
therefore it must appear before ‘--’)
Special care should be taken when using mtasim from root
account, especially if used with -Xauto and
--statedir. The mailfromd utility executed by it
will switch to privileges of the user given in its configuration
(see Starting and Stopping) and will not be able to create data in
its state directory, because the latter was created using ‘root’
as owner. To help in this case, mtasim understands
--user and --group command line options, that have
the same meaning as for mailfromd.
Now, let’s try HELP command again:
250-mtasim (mailfromd 8.14); supported SMTP commands: 250- EHLO 250- HELO 250- MAIL 250- RCPT 250- DATA 250- HELP 250- QUIT 250- HELP 250- RSET 250-Supported administrative commands: 250- \Dname=value [name=value...] Define Sendmail macros 250- \Ecode Expect given SMTP reply code 250- \L[name] [name...] List macros 250- \Uname [name...] Undefine Sendmail macros 250 \Sfamily hostname address [port] Define sender socket address
While the SMTP commands do not need any clarification, some words about the administrative commands are surely in place. These commands allow to define, undefine and list arbitrary Sendmail macros. Each administrative command consists of a backslash followed by a command letter. Just like SMTP ones, administrative commands are case-insensitive. If a command takes arguments, the first argument must follow the command letter without intervening whitespace. Subsequent arguments can be delimited by arbitrary amount of whitespace.
For example, the \D command defines Sendmail macros:
(mtasim) \Dclient_addr=192.168.10.1 f=sergiusz@localhost i=testmsg (mtasim)
Notice that mailfromd does not send any response to the
command, except if there was some syntactic error, in which case it
will return a ‘502’ response.
Now, you can list all available macros:
(mtasim) \L 220-client_addr=192.168.10.1 220-f=sergiusz@localhost 220 i=testmsg (mtasim)
or just some of them:
(mtasim) \Lclient_addr 220 client_addr=192.168.10.1 (mtasim)
To undefine a macro, use \U command:
(mtasim) \Ui (mtasim) \l 220-client_addr=192.168.10.1 220 f=sergiusz@localhost (mtasim)
The \S command declare sender socket and host name. These
parameters are passed to the connect handler, if one is
declared (see connect handler). To give you a chance to use this
command, mtasim does not invoke connect handler right
after connecting to the milter. Instead it waits until either the
\S command or any SMTP command (except ‘HELP’)
is given. After calling connect handler the \S is
disabled (to reflect it, it also disappears from the HELP
output).
The \S command takes 1 to 4 arguments. The first argument
supplies the socket family (see Table 4.3). Allowed values
are: ‘stdio’, ‘unix’, ‘inet’, ‘inet6’ or
numbers from ‘0’ to ‘3’.
The \S stdio (or \S 0) command needs no additional
arguments. It indicates that the SMTP connection is
obtained from the standard input. It is the default if sender socket
is not declared explicitly.
The command \S unix indicates that the connection is accepted
from a UNIX socket. It requires two more argument. The first one
supplies sender host name and the second one supplies full
path name of the socket file. For example:
\S unix localhost /var/run/smtp.sock
The commands \S inet and \S inet6 indicate that the
connection came from an ‘INET’ IPv4 or IPv6 socket,
correspondingly29. They require all
four arguments to be specified. The additional arguments are:
host name, IP address, and port number, in that order. For example:
\S inet relay.gnu.org.ua 213.130.31.41 34567
or
\S inet6 relay.gnu.org.ua 2001:470:1f0a:1be1::2 34567
Sender socket address can also be configured from the command line (see sender-socket).
Now, let’s try a real-life example. Suppose you wish to test the
greylisting functionality of the filter script described in Filter Script Example. To do this, you start mtasim:
$ mtasim -Xauto -- -I. -I../mflib test.rc 220-mtasim (mailfromd 8.14) ready 220 Connected to milter unix:/tmp/mtasim-ak3DEc/socket (mtasim)
The script in test.rc needs to know client_addr macro,
so you supply it to mtasim:
(mtasim) \Dclient_addr=10.10.1.13
Now, you try an SMTP session:
(mtasim) ehlo yahoo.com 250-pleased to meet you 250 HELP (mtasim) mail from: <gray@yahoo.com> 250 Sender OK (mtasim) rcpt to: <gray@localhost> 450 4.7.0 You are greylisted for 300 seconds
OK, this shows that the greylisting works. Now quit the session:
(mtasim) quit 221 Done
Mailfromd Manual:
mtasim expect commandsUntil now we were using mtasim interactively. However, it
is often useful in shell scripts, for example the mailfromd
test suite is written in shell and mtasim. To avoid the
necessity to use auxiliary programs like expect or
DejaGNU, mtasim contains a built-in expect
feature. The administrative command \E introduces the
SMTP code that the next command is expected to yield. For
example,
\E250 rcpt to: <foo@bar.org>
tells mtasim that the response to RCPT TO command
must begin with ‘250’ code. If it does, mtasim
continues execution. Otherwise, it prints an error message and
terminates with exit code 1. The error message it prints looks like:
Expected 250 but got 470
The expect code given with the \E command may have less than
3 digits. In this case it specifies the first digits of expected
reply. For example, the command ‘\E2’ matches replies
‘200’, ‘220’, etc.
This feature can be used to automate your tests. For example, the following script tests the greylisting functionality (see the previous section):
# Test the greylisting functionality
#
\E220
\Dclient_addr=10.10.1.13
\E250
ehlo yahoo.com
\E250
mail from: <gray@yahoo.com>
\E450
rcpt to: <gray@localhost>
\E221
quit
This example also illustrates the fact that you can use
‘#’-style comments in the mtasim input. Such a script
can be used in shell programs, for example:
mtasim -Xauto --statedir -- -I. -I../mflib test.rc < scriptfile if $? -ne 0; then echo "Greylisting test failed" fi
Mailfromd Manual:
It is possible to log an entire SMTP session to a file. This is called session tracing. Two options are provided for this purpose:
Sets the name of the trace file, i.e. a file to which the session
transcript will be written. Both the input commands, and the
mtasim responses are logged. If the file file exists,
it will be truncated before logging. This, however, can be changed
using the following option:
If the trace file exists, append new trace data to it.
Mailfromd Manual:
To start mtasim in daemon mode, use the
--daemon (or -bd) command line option. This mode
is not quite the same as Sendmail -bd mode. When started in
daemon mode, mtasim selects the first available
TCP port to use from the range ‘1024 -- 65535’.
It prints the selected port number on the standard output and
starts listening on it. When a connection comes, it serves a
single SMTP session and exits immediately when it is
ended.
This mode is designed for use in shell scripts and automated test cases.
Mailfromd Manual:
mtasim Administrative CommandsThis section provides a summary of administrative commands available
in mtasim.
Defines Sendmail macro name to the given value. Any number of name=value pairs can be given as arguments.
See D command.
Instructs mtasim to expect next SMTP command to
return given code (a three-digit decimal number).
See expect commands.
Lists defined macros. See L command.
Undefines macros given as its arguments.
Declares the sender socket parameters. See S command, for a detailed description and examples.
This command is available only at the initial stage of a
mtasim session, before the first SMTP command was
given. It is disabled if the --sender-socket option was
given in the command line (see sender-socket).
The help output reflects whether or not this command is available.
If neither this command nor the --sender-socket option were
given, mtasim behaves as if given the \S stdio
command.
The family argument
supplies the socket family, i.e. the first argument to the
connect handler (see connect handler). It can have either
literal or numeric value, as described in the table below:
| Literal | Numeric | Meaning |
|---|---|---|
| stdio | 0 | Standard input/output (the MTA is run with -bs option) |
| unix | 1 | UNIX socket |
| inet | 2 | IPv4 protocol |
| inet6 | 3 | IPv6 protocol |
Table 12.1: Socket families
See also Table 4.3.
Depending on the family, the rest of arguments supply additional parameters:
The hostname argument can be specified. It defines the first
argument of the connect handler (see hostname in connect handler).
All arguments must be specified.
| argument | connect argument | meaning |
|---|---|---|
| hostname | 1 | Sender host name |
| address | 4 | Sender IP address |
| port | 3 | Sender port number |
Hostname and address must be supplied. The address argument must be a full pathname of the UNIX socket.
Mailfromd Manual:
mtasim command line optionsThis section summarizes all available mtasim command line options.
Append to the trace file. See traces.
Set the body chunk length (bytes) for xxfi_body calls.
Run as daemon. See daemon mode.
Define Sendmail macro macro to the given value. It is
similar to the \D administrative command (see D command)
Set desired logging level for gacopyz library
(see Gacopyz). See gacopyz-log option, for a detailed
description of level. Notice, that unless this option is used,
the --verbose (-v) command line option implies
--gacopyz-log=debug.
When switching to user’s privileges as requested by the --user command line option, retain the additional group name. Any number of --group options may be given to supply a list of additional groups.
Run with this user privileges. This option and the --group
option have effect only if mtasim was started with root
privileges.
Display a short help summary
Force using the given Milter protocol version number. The version argument is either a numeric version (e.g. ‘2’), or a version string in form ‘major.minor[.patch]’, where square brackets indicate optional part. The default is ‘1.0.0’. If version is any of ‘2’, ‘3’ or ‘1.0.0’, the default protocol capabilities and actions for that version are set automatically. This option is intended for development and testing of the Gacopyz library (see Gacopyz).
Set Milter protocol capabilities. See gacopyz/gacopyz.h for the meaning of various bits in the bitmask. Look for the C macros with the prefix ‘SMFIP_’.
Set timeouts for various Milter operations. Values is a comma-separated list of assignments ‘T=V’, where T is a timeout code, indicating which timeout to set, and V is its new value. Valid timeout codes are:
Timeout for connecting to a filter.
Timeout for sending information from the simulator to a filter.
Timeout for reading reply from the filter.
Overall timeout between sending end-of-message to filter and receiving
final acknowledgment. Indirectly, it configures the upper
limit on the execution time of the eom handler (see eom handler).
Set Milter actions. See gacopyz/gacopyz.h for the meaning of various bits in the bitmask. Look for the C macros with the prefix ‘SMFIF_’.
Not-interactive mode (disable readline). See Command Line Editing in GNU Readline Library.
Communicate with given Milter port. See mtasim milter port.
Set readline prompt. The default prompt string is ‘(mtasim) ’.
Declare sender socket address. This option has the same effect as
the S command. See S command, for a detailed discussion
and a description of its arguments.
When using -Xauto, use the temporary directory name as
mailfromd state directory (see statedir mtasim option).
Use the SMTP protocol on standard input and output. This
is the default mode for mtasim. See interactive mode.
Set name of the trace file. See traces.
Display option summary
Increase verbosity level. Implies --gacopyz-log=debug, unless that option is used explicitly.
Print program version
Mailfromd Manual:
Pmult is a Pmilter–Milter multiplexer, i.e. a
program that acts as a mediator between the Pmilter server
and one or several Milter clients. Usually, the former is
an instance of smtps from MeTA1, and the latter are running
mailfromd instances. Pmult receives Pmilter
commands from the server, translates them into equivalent Milter
commands and passes the translated requests to a preconfigured set of
Milter filters. When the filters reply, the reverse operation is performed:
Milter responses are translated into their Pmilter equivalents and
are sent back to the server.
+-----------------+
+----->| Milter Client 1 |
| +-----------------+
|
+-----------+ +---------+ | +-----------------+
| MeTA1 |<=====>| Pmult |<--+----->| Milter Client 1 |
+-----------+ +---------+ | +-----------------+
|
+---------> //
|
| +-----------------+
+----->| Milter Client N |
+-----------------+
Due to the specifics nature of the threaded MeTA1 libraries,
pmult does not detach from the controlling terminal
(i.e. does not become a daemon). To run it as a background process,
we recommend to use pies daemon. ‘Pies’ is a powerful
utility that allows you to launch several foreground-designed programs
in the background and control their execution. See Pies in Pies Manual, for a detailed description of the program.
For a practical advice on how to use it with pmult, see
Using Pies to Run Pmult in Pies Manual. For
a description on how to start both pmult and MeTA1 from
the same pies configuration file, see Using
Pies to Run Pmult and MeTA1 in Pies Manual.
Mailfromd Manual:
Pmult reads its configuration from the main configuration
file /etc/mailfromd.conf. Unless it is the only component of
the ‘Mailfromd’ package that is being run, its configuration
should be explicitly marked as such by using either program or
include statement, as described in Mailfromd Configuration.
The following standard Mailutils statements are understood:
| Statement | Reference |
|---|---|
| debug | See Mailutils Configuration File in GNU Mailutils Manual. |
| logging | See Mailutils Configuration File in GNU Mailutils Manual. |
| include | See Mailutils Configuration File in GNU Mailutils Manual. |
Mailfromd Manual:
Pmult listens for Pmilter requests on a socket, configured
using listen statement:
Listen on the given url. Argument is a valid Mailutils URL. See milter port specification, for a description of url.
Since pmult runs as a foreground program, it does not write
its PID number to a file by default. If this behavior is required, it
can be enabled using the following statement:
Store PID of the pmult process in file.
The following three limits require MeTA1 version ‘PreAlpha30.0’ or later.
“Soft” limit on the number of ‘pmilter’ threads. Default is 2.
“Hard” limit on the number of ‘pmilter’ threads. This is
roughly equivalent to the number of emails pmult is able
to handle simultaneously. The default value is 6. Raise this limit
if you experience long delays when connecting to the SMTP port.
Maximum number of file descriptors ‘pmilter’ library is allowed to open simultaneously. Default is 10.
Mailfromd Manual:
MeTA1’s notion of macros differs considerably from that of Sendmail.
Macros in MeTA1 are identified by integer numbers and only a limited
number of macros can be provided for each Pmilter stage.
Pmilter stages mostly correspond to Milter states (see handler names), except that there are no distinct header and body stages,
instead these two are combined into a single ‘data’ stage. This
comes unnoticed to mailfromd scripts, because pmult takes
care to invoke right Milter handlers within the single ‘data’
Pmilter state. Therefore in the discussion that follows we will refer
to Mailfromd handlers, rather than to Pmilter stages.
The most important standard Milter macros are always provided by
pmult itself. These are:
The IP address of the SMTP client. As of version 8.14, only IPv4 addresses are supported. Defined in all handlers.
The port number of the SMTP client. Defined in all handlers.
MeTA1 session ID. Defined in all handlers.
The envelope sender (from) address. Defined in envfrom and
subsequent handlers.
The number of bad recipients for a single message. Defined in
envfrom and envrcpt handlers.
The number of delivery attempts. As of version 8.14 it is
always ‘1’. Defined in envfrom and subsequent handlers.
The number of validated recipients for a single message. Defined in
envfrom and envrcpt handlers.
Protocol used to receive the message. The value of this macro is always ‘SMTP’. Defined in all handlers.
The host from the resolved triple of the address given for the SMTP
RCPT command. Defined in envrcpt handler.
The address part of the resolved triple of the address given for the
SMTP RCPT command. Defined in envrcpt handler.
Sender’s helo domain (parameter to EHLO or HELO
command).
Two additional macros are provided for all handlers that allow to
identify whether the message is processed via pmult:
Canonical name of the multiplexer program, i.e. ‘pmult’.
Version of pmult.
These macros can be used in mailfromd filters to provide alternative processing for messages coming from a MeTA1 server.
Macros defined in MeTA1 can be made available in Mailfromd handlers
using the define-macros statement.
Define a set of Sendmail macros for the given Mailfromd handler. Allowed values for handler are: ‘connect’, ‘helo’, ‘mail’ (or ‘envfrom’), ‘rcpt’ (or ‘envrcpt’), ‘data’ (or ‘header’ or ‘body’), ‘dot’ (‘eom’). A list of these values is also accepted, in which case macros are defined for each handler from the list.
The second argument specifies a list of names of the macros that should be defined in this handler. Allowed macro names are:
Hostname of SMTP server.
Result of client lookup.
TLS/SSL version used.
TLS cipher suite used.
Effective key length of the symmetric encryption algorithm.
The DN (distinguished name) of the presented certificate.
The DN (distinguished name) of the CA (certificate authority) that signed the presented certificate (the cert issuer).
Maximum key length of the symmetric encryption algorithm. This may be less than the effective key length for export controlled algorithms.
The result of the verification of the presented cert.
The CN (common name) of the presented certificate.
The CN (common name) of the CA that signed the presented certificate.
The mechanism used for SMTP authentication (only set if successful).
The client’s authentication credentials as determined by authentication (only set if successful). The actual format depends on the mechanism used, it might be just ‘user’, or ‘user@realm’, or something similar.
The authorization identity, i.e. the ‘AUTH=’ parameter of the SMTP MAIL command if supplied.
MeTA1 transaction id.
Message-Id of the message.
The hop count. Basically, this is the number of ‘Received:’ headers.
Notice the following limitations:
STARTTLS
command.
PM_MAX_MACROS define in include/sm/pmfdef.h. In MeTA1
versions up to and including 1.0.PreAlpha28.0, this number is 8. If
you need more macros, increase this number and recompile MeTA1.
If bool is true (see boolean in GNU Mailutils Manual), pass auth macros to mailfromd ‘mail’
handler. It is equivalent to:
define-macros mail (auth_type, auth_authen, auth_author);
Mailfromd Manual:
In pmult terminology, remote Milters are clients.
The number of clients pmult is able to handle is not
limited. Each client is declared using client statement:
client [ident] {
# Set remote protocol type.
type protocol-type;
# Set remote client URL.
url arg;
# Set write timeout.
write-timeout duration;
# Set read timeout.
read-timeout duration;
# Set timeout for EOM.
eom-timeout duration;
# Set connect timeout.
connect-timeout duration;
# Set log verbosity level.
log-level level;
};
Declare a Milter client. Optional ident gives the identifier of this client, which will be used in diagnostics messages.
Statements are described below.
This statement is reserved for future use. In version 8.14 it is a no-op.
If given, the value of typestr must be ‘milter’.
In future versions this statement will declare the protocol to be used to interact with this client. The syntax for typestr is
type [version]
where type is either ‘milter’ or ‘pmilter’, and optional version is minimal protocol version.
Set remote client URL. See milter port specification, for a description of url.
Configure Milter initial connection timeout. Default is 300.
See time interval specification, for information on interval format.
Configure Milter write timeout. Default is 10.
See time interval specification, for information on interval format.
Configure Milter read timeout. Default is 10.
See time interval specification, for information on interval format.
Configure Milter end of message timeout. Default is 300.
See time interval specification, for information on interval format.
Set Milter log verbosity level for this client. Argument is a list of items separated by commas or whitespace. Each item is a log level optionally prefixed with ‘!’ to indicate “any level except this”, ‘<’, meaning “all levels up to and including this”, or with ‘>’, meaning “all levels starting from this”.
Log levels in order of increasing priority are: ‘proto’, ‘debug’,
‘info’, ‘warn’, ‘err’, ‘fatal’. The first two
levels are needed for debugging libgacopyz and Milter protocol.
See Gacopyz, for the description of the libgacopyz library.
See also the following subsection.
Mailfromd Manual:
If needed, pmult can be instructed to provide additional
debugging information. The amount of this information is configured
by three configuration statements. First of all, the standard
debug block statement controls debugging of the underlying GNU
Mailutils libraries (see Mailutils Configuration
File in GNU Mailutils Manual). Secondly, the debug
statement controls debugging output of the pmult utility
itself. The pmilter-debug statement controls debugging output
of the underlying MeTA1 libraries, and, finally, the log-level
statement, described in the previous subsection, defines debugging
level for the Milter library (libgacopyz).
Set debugging level for the pmult code. See Mailutils Configuration File in GNU Mailutils
Manual, for a description of spec syntax. Multiplexor-specific
debugging is enabled by the ‘pmult’ category. The following
levels are used:
Prints the following information:
Information about milter to Pmilter request translation.
Detailed dump of message body chunks received during Pmilter ‘DATA’ stage.
Logs bad recipient addresses.
This information is printed using the output channel defined in the
logging statement (see Mailutils Configuration File in GNU Mailutils Manual).
Set debug verbosity level for the Pmilter library. Argument is a positive integer between zero (no debugging, the default), and 100 (maximum debugging).
Pmilter debugging information is printed on the standard error. Use
pies stderr statement to capture this stream and
redirect it to the syslog or file (see Output Redirectors in Pies Manual).
Mailfromd Manual:
The following is an example of a working pmult
configuration. The multiplexer listens on localhost, port
‘3333’. It prints its diagnostics using syslog facility
local2. A single Mailfromd client is declared, which
listens on UNIX socket
/usr/local/var/mailfromd/mailfrom. The log verbosity level
for this client is set to ‘info’ and higher, i.e.: ‘info’,
‘warn’, ‘err’ and ‘fatal’.
listen inet://127.0.0.1:3333;
logging {
facility local2;
};
debug {
level "pmult.trace7";
}
define-macros envmail (auth_type, auth_authen, auth_author, tls_vrfy);
define-macros envrcpt (auth_type, auth_authen, auth_author);
client {
type milter;
url /usr/local/var/mailfromd/mailfrom;
log-level ">info";
# Set write timeout.
write-timeout 30 seconds;
# Set read timeout.
read-timeout 5 minutes;
# Set timeout for EOM.
eom-timeout 5 minutes;
}
Mailfromd Manual:
Normally, pmult is invoked without command line
arguments. However, it does support several command line options.
First of all, the common GNU Mailutils options are understood, which
are useful for checking pmult configuration file for syntax
errors. See Common Options in GNU
Mailutils Manual, for a detailed description of these.
The rest of command line options supported by pmult is
useful mostly for debugging. These options are summarized in the
table below:
Set the identifier used in syslog messages to string. This
option mostly is for debugging purposes. We advise
to use logging configuration statement for this purpose
(see Logging Statement in GNU Mailutils Manual).
Disable signal handling in the main thread. This is for debugging purposes.
Log to the syslog. This is the default. See Logging Statement in GNU Mailutils Manual, for information on how to configure syslog logging.
Log to the standard error stream.
Listen on the given url. This overrides the url
configuration statement (see url).
Set debug verbosity level. This overrides the debug
configuration statement. See pmult-debug, for more information.
Mailfromd Manual:
Documentation is like sex: when it is good, it is very, very good; and when it is bad, it is better than nothing.
Dick Brandon
Although the author has tried to make this documentation as detailed as is possible and practical, he is well aware that the result is rather “better than nothing”, than “very good”. So, if you find that some piece of explanation is lousy or if you find anything that should have been mentioned here, but is not, please report it to bug-mailfromd@gnu.org.ua.
Similarly, if the program itself fails to meet your expectations, or
does not do what is described in this document; if you have found a
bug or happen to have any suggestion... or have written a useful
function you wish to share with the rest of mailfromd users,
or wish to express your thanks, email it to the same address,
bug-mailfromd@gnu.org.ua.
If you think you’ve found a bug, please be sure to include maximum information needed to reliably reproduce it, or at least to analyze it. The information needed is:
Mailfromd Manual:
Gacopyz, panie, to mówią ze to mysa... Ze to tako mysa co świeckę w kościele zjadła i wniebowstąpienia dostąpiła. A to nie je mysa, ino gacopyz! To nadprzyrodzłyne, to głową na dół śpi!
Kazimierz Grześkowiak
‘Gacopyz’ is the client library implementing Milter protocol.
It differs considerably from the Sendmail implementation and offers a
new and more flexible API. The old API is
supported for compatibility with libmilter.
The library name comes from the song ‘Rozprawa o robokach’ by Kazimierz Grzeskowiak. The phrase ‘A to nie je mysa, ino gacopyz’ exactly describes what the library is: ‘That is no libmilter, but gacopyz’.
Future versions of this documentation will include a detailed description of the library.
Mailfromd Manual:
This appendix documents the time format specifications understood by
the command line option --time-format
(see --time-format). Essentially, it is a reproduction of the man
page for GNU strftime function.
Ordinary characters placed in the format string are reproduced without conversion. Conversion specifiers are introduced by a ‘%’ character, and are replaced as follows:
| %a | The abbreviated weekday name according to the current locale. |
| %A | The full weekday name according to the current locale. |
| %b | The abbreviated month name according to the current locale. |
| %B | The full month name according to the current locale. |
| %c | The preferred date and time representation for the current locale. |
| %C | The century number (year/100) as a 2-digit integer. |
| %d | The day of the month as a decimal number (range 01 to 31). |
| %D | Equivalent to ‘%m/%d/%y’. |
| %e | Like ‘%d’, the day of the month as a decimal number, but a leading zero is replaced by a space. |
| %E | Modifier: use alternative format, see below (see conversion specs). |
| %F | Equivalent to ‘%Y-%m-%d’ (the ISO 8601 date format). |
| %G | The ISO 8601 year with century as a decimal number. The 4-digit year corresponding to the ISO week number (see ‘%V’). This has the same format and value as ‘%y’, except that if the ISO week number belongs to the previous or next year, that year is used instead. |
| %g | Like ‘%G’, but without century, i.e., with a 2-digit year (00-99). |
| %h | Equivalent to ‘%b’. |
| %H | The hour as a decimal number using a 24-hour clock (range 00 to 23). |
| %I | The hour as a decimal number using a 12-hour clock (range 01 to 12). |
| %j | The day of the year as a decimal number (range 001 to 366). |
| %k | The hour (24-hour clock) as a decimal number (range 0 to 23); single digits are preceded by a blank. (See also ‘%H’.) |
| %l | The hour (12-hour clock) as a decimal number (range 1 to 12); single digits are preceded by a blank. (See also ‘%I’.) |
| %m | The month as a decimal number (range 01 to 12). |
| %M | The minute as a decimal number (range 00 to 59). |
| %n | A newline character. |
| %O | Modifier: use alternative format, see below (see conversion specs). |
| %p | Either ‘AM’ or ‘PM’ according to the given time value, or the corresponding strings for the current locale. Noon is treated as ‘pm’ and midnight as ‘am’. |
| %P | Like ‘%p’ but in lowercase: ‘am’ or ‘pm’ or a corresponding string for the current locale. |
| %r | The time in ‘a.m.’ or ‘p.m.’ notation. In the POSIX locale this is equivalent to ‘%I:%M:%S %p’. |
| %R | The time in 24-hour notation (‘%H:%M’). For a version including the seconds, see ‘%T’ below. |
| %s | The number of seconds since the Epoch, i.e., since 1970-01-01 00:00:00 UTC. |
| %S | The second as a decimal number (range 00 to 61). |
| %t | A tab character. |
| %T | The time in 24-hour notation (‘%H:%M:%S’). |
| %u | The day of the week as a decimal, range 1 to 7, Monday being 1. See also ‘%w’. |
| %U | The week number of the current year as a decimal number, range 00 to 53, starting with the first Sunday as the first day of week 01. See also ‘%V’ and ‘%W’. |
| %V | The ISO 8601:1988 week number of the current year as a decimal number, range 01 to 53, where week 1 is the first week that has at least 4 days in the current year, and with Monday as the first day of the week. See also ‘%U’ and ‘%W’. |
| %w | The day of the week as a decimal, range 0 to 6, Sunday being 0. See also ‘%u’. |
| %W | The week number of the current year as a decimal number, range 00 to 53, starting with the first Monday as the first day of week 01. |
| %x | The preferred date representation for the current locale without the time. |
| %X | The preferred time representation for the current locale without the date. |
| %y | The year as a decimal number without a century (range 00 to 99). |
| %Y | The year as a decimal number including the century. |
| %z | The time-zone as hour offset from GMT. Required to emit RFC822-conformant dates (using ‘%a, %d %b %Y %H:%M:%S %z’) |
| %Z | The time zone or name or abbreviation. |
| %+ | The date and time in date(1) format. |
| %% | A literal ‘%’ character. |
Some conversion specifiers can be modified by preceding them by the ‘E’ or ‘O’ modifier to indicate that an alternative format should be used. If the alternative format or specification does not exist for the current locale, the behaviour will be as if the unmodified conversion specification were used. The Single Unix Specification mentions ‘%Ec’, ‘%EC’, ‘%Ex’, ‘%EX’, ‘%Ry’, ‘%EY’, ‘%Od’, ‘%Oe’, ‘%OH’, ‘%OI’, ‘%Om’, ‘%OM’, ‘%OS’, ‘%Ou’, ‘%OU’, ‘%OV’, ‘%Ow’, ‘%OW’, ‘%Oy’, where the effect of the ‘O’ modifier is to use alternative numeric symbols (say, roman numerals), and that of the ‘E’ modifier is to use a locale-dependent alternative representation.
Mailfromd Manual:
The following sections describe procedures for upgrading between the consecutive Mailfromd releases. The absence of a section for a pair of versions x-y numbers means that no specific actions are required for upgrading from x to y.
Mailfromd Manual:
No special actions are required. There are several important changes
in version 8.14, most notable ones being improved dkim_sign
function, DNS resolver tolerance for CNAME chains, and buffered I/O.
This change is important for those who use dkim_sign with
Sendmail. See dkim_sign and sendmail, for a detailed discussion.
Mailfromd dropped support for CNAME chains in version 8.3
(see 820-830). This change was forced by the behavior of
the adns resolver library, which had apparently been grounded
on somewhat rigorous reading of RFCs
103430
and
218131.
Reportedly, many existing DNS servers still employ CNAME chains leading to
TXT records (in particular, to DKIM TXT records), so this change made certain
DKIM signatures unverifiable for mailfromd.
To fix this, starting from version 8.14 mailfromd implements
a work-around that allows it to follow CNAME chains of limited
length. The default length is 2 (which means CNAME pointing to a
CNAME, pointing to a valid RR). It can be changed using the
dns.max-cname-chain configuration statement
(see conf-resolver).
Buffered I/O can tremendously improve performance of getdelim
and getline.
The global variables io_buffering and io_buffer_size
(see io_buffering) define buffering mode and associated buffer
size for file descriptors returned by the subsequent calls to
open or spawn. Buffering mode of an already open file
descriptor can be changed using the setbuf function.
The io_buffering variable defines the buffering mode. By
default it is 0 (BUFFER_NONE), which disables buffering for
backward compatibility with the previous versions. Another
possible values are: 1 (BUFFER_FULL) and 2 (BUFFER_LINE).
When set to BUFFER_FULL, all I/O operations become fully buffered.
The buffer size is defined by the io_buffer_size global variable.
BUFFER_LINE is similar to BUFFER_FILE when used for
input. When used for the output, the data are accumulated in buffer
and actually sent to the underlying transport stream when the newline
character is seen. The io_buffer_size global variable sets the
initial value for the buffer size in this mode. The actual size can
grow as needed during the I/O.
The default value for io_buffer_size is the size of the system page.
The symbolic constants BUFFER_NONE, BUFFER_FULL and
BUFFER_LINE are defined in the status.mf module. E.g.:
require status
begin
do
io_buffering = BUFFER_FULL
done
will set up all the subsequent buffer-aware I/O functions for buffered reads and writes using the maximum buffer capacity.
The setbuf function (see setbuf) changes the buffering
mode and/or buffer size for an already opened stream, e.g.:
setbuf(fd, BUFFER_FULL, 4096)
For detailed discussion of various buffering modes and their effect on the I/O, see I/O functions.
Mailfromd Manual:
DKIM support (see DKIM) introduced in this version requires the
Nettle cryptographic
library32. It you
need DKIM, make sure Nettle is installed prior to compiling
mailfromd. Otherwise, no special actions are required.
Mailfromd Manual:
New configure option --with-dbm allows you to select any
DBM flavor supported by GNU mailutils as the default DBM implementation
for mailfromd.
Mailfromd Manual:
Versions 8.3 and 8.4 differ only in required minimal version of mailutils (3.3 and 3.4, correspondingly). Apart from that, the following instructions apply to both versions.
In version 8.3 I abandoned the legacy DNS resolver and switched to GNU adns. GNU ands is a standalone resolver library, which provides a number of advanced features. It is included in most distributions. The source code of the recent release is available from http://www.chiark.greenend.org.uk/~ian/adns/adns.tar.gz.
This change brought a number of user-visible changes. In particular, arbitrary limits on the sizes of the RRs are removed. Consequently, the following configurations statements are withdrawn:
runtime.max-dns-reply-aruntime.max-dns-reply-ptrruntime.max-dns-reply-mxmax-match-mxmax-callout-mxSecondly, the new resolver is less tolerant to deviations from the standard. This means that remote DNS misconfigurations that would have slipped unnoticed in previous versions, will be noticed by mailfromd 8.3. For example, a CNAME record pointing to another CNAME is treated as an error.
A new command line option was added to mailfromd and
calloutd: --resolv-conf-file. This option instructs
the programs to read resolver settings from the supplied file, instead
of the default /etc/resolv.conf.
Another user-visible change is in handling of SPF checks. Previously, results if SPF checks were cached in a database. This proved to cause more problems than solutions and was removed in this version. As a result, the following MFL global variables have been withdrawn:
spf_ttlspf_cachedspf_databasespf_negative_ttl
Mailfromd Manual:
Version 8.0 is a major rewrite, that introduces a lot of new concepts and features. Nevertheless, it is still able to run the MFL scripts from version 7.0 without modifications.
Note the following important points:
listen configuration statement withdrawn
Use the server milter statement instead. See conf-server.
This option was a noop since version 7.0.91.
The ‘%’ characters is used as modulo operator. See Arithmetic operations.
debug_spec built-in function changed signature.
See debug_spec.
listens and portprobe
The listens function was moved to the portprobe module. It is
actually an alias to the portprobe function. If your filter uses
listens, make sure to require the portprobe
module.
See portprobe.
_pollhost, _pollmx, stdpoll, strictpoll
These functions have been moved to the poll module, which must be required prior to using any of them.
message_header_count function.
This function takes an optional string argument, supplying the header name. See message_header_count.
Mailfromd Manual:
The release 7.0 removes the features which were declared as obsolete in 6.0 and introduces important new features, both syntactical, at the MFL level, and operational.
Unless your filter used any deprecated features, it should work correctly after upgrade to this version. It will, however, issue warning messages regarding the deprecated features (e.g. the use of ‘%’ in front of identifiers, as described below). To fix these, follow the upgrade procedure described in upgrade procedure.
The removed features are:
The MFL syntax has changed: it is no longer necessary to use ‘%’ in front of a variable to get its value. To reference a variable, simply use its name, e.g.:
set x var + z
The old syntax is still supported, so the following statement will also work:
set x %var + %z
It will, however, generate a warning message.
Of course, the use of ‘%’ to reference variables within a string literal remains mandatory.
Another important changes to MFL are user-defined exceptions (see User-defined Exceptions) and the try–catch construct (see try–catch).
Several existing MFL functions have been improved. In
particular, it is worth noticing that the open function, when
opening a pipe to or from a command, provides a way to control where
the command’s standard error would go (see standard error).
The accept function (or action) issues a warning if its use would
cancel any modifications to the message applied by, e.g.,
header_add and similar functions. See Message modification queue, for a detailed discussion of this feature.
The most important change in mailfromd operation is that
the version 7.0 is able to run several servers (see conf-server).
Dedicated callout servers make it possible to run sender
verifications in background, using a set of long timeouts, as
prescribed by RFC 2822 (see SMTP Timeouts). This diminishes
the number of false positives, allows for coping with servers showing
large delays and also reduces the number of callouts performed for
such servers.
This release no longer includes the smap utility. It was
moved into a self-standing project, which by now provides much more
functionality and is way more flexible than this utility was. If you
are interested in using smap, visit
http://www.gnu.org.ua/software/smap, for a detailed
information, including pointers to file downloads.
Mailfromd Manual:
The 6.0 release is aimed to fix several logical inconsistencies that
affected the previous versions. The most important one is that until
version 5.2, the filter script file contained both the actual filter
script, and the run-time configuration for mailfromd (in
form of ‘#pragma option’ and ‘#pragma database’ statements).
The new version separates run-time configuration from the
filter script by introducing a special configuration file
mailfromd.conf (see Mailfromd Configuration).
Consequently, the ‘#pragma option’ and ‘#pragma database’ statements become deprecated. Furthermore, the following deprecated pragmas are removed: ‘#pragma option ehlo’, ‘#pragma option mailfrom’. These pragmas became deprecated in version 4.0 (see 31x-400).
The second problem was that the default filter script file had ‘.rc’ suffix, which usually marks a configuration file, not the source. In version 6.0 the script file is renamed to mailfromd.mf. In the absence of this file, the legacy file mailfromd.rc is recognized and parsed. This ensures backward compatibility.
This release also fixes various inconsistencies and dubious features in the MFL language.
The support for unquoted literals is discontinued. This feature was marked as deprecated in version 3.0.
The following features are deprecated: ‘#pragma option’ (pragma-option and ‘#pragma database’ (pragma-database) directives, the legacy style of function declarations (old-style function declarations), calls to functions of one argument without parentheses (operational notation), the ‘#require’ statement (See import, for the new syntax) and implicit concatenation (implicit concatenation). See Deprecated Features, for more information about these.
This release also introduces important new features, which are summarized in the table below:
| Feature | Reference |
|---|---|
| Configuration | See Mailfromd Configuration. |
| Module system | See Modules. |
| Explicit type casts | See explicit type casts. |
| Concatenation operator | See Concatenation. |
| Scope of visibility | See scope of visibility. |
| Precious variables | See rset. |
Mailfromd version ‘6.0’ will work with unchanged
scripts from ‘5.x’. When started, it will verbosely warn you
about any deprecated constructs that are used in your filter sources
and will create a script for upgrading them.
To upgrade your filter scripts, follow the steps below:
mailfromd: Warning: using legacy script file /usr/local/etc/mailfromd.rc mailfromd: Warning: rename it to /usr/local/etc/mailfromd.mf or use script-file statement in /usr/local/etc/mailfromd.conf to disable this warning mailfromd: /usr/local/etc/mailfromd.rc:19: warning: this pragma is deprecated: use relayed-domain-file configuration statement instead mailfromd: /usr/local/etc/mailfromd.rc:23: warning: this pragma is deprecated: use io-timeout configuration statement instead mailfromd: Info: run script /tmp/mailfromd-newconf.sh to fix the above warnings …
mailfromd will create a shell script
/tmp/mailfromd-newconf.sh for fixing these warnings. Run it:
$ sh /tmp/mailfromd-newconf.sh
mailfromd --lint again. If
it shows no more deprecation warnings, the conversion went correctly.
Now you can remove the upgrade script:
$ rm /tmp/mailfromd-newconf.sh
Notice, that the conversion script attempts to fix only deprecation warnings. It will not try to correct any other type of warnings or errors. For example, you may get warning messages similar to:
mailfromd: /etc/mailfromd.mf:7: warning: including a module file is unreliable and may cause subtle errors mailfromd: /etc/mailfromd.mf:7: warning: use `require dns' instead
This means that you use ‘#include’ where you should have used ‘require’. You will have to fix such warnings manually, as suggested in the warning message.
If, for some reason, you cannot upgrade your scripts right now, you
may suppress deprecation warnings by setting the environment variable
MAILFROMD_DEPRECATION to ‘no’ before starting
mailfromd. Nonetheless, I recommend to upgrade as soon as
possible, because the deprecated features will be removed in version
‘6.1’.
Mailfromd Manual:
Upgrading from 5.0 to 5.1 does not require any changes in your filter scripts. Notice, however, the following important points:
mailfromd supports Milter
protocol version 6, which is compatible with Sendmail 8.14.0 and
newer. While being backward compatible with earlier Sendmail
releases, it allows you to use the new ‘prog data’ handler
(see data). It also supports macro negotiation, a
feature that enables Mailfromd to ask MTA to export the
macros it needs for each particular handler. This means that if you
are using Sendmail 8.14.0 or higher (or Postfix 2.5 or higher), you no
longer need to worry about exporting macro names in sendmail.cf
file.
The same feature is also implemented on the server side, in
mtasim and pmult. Consequently, using
define-macros in pmult configuration file
is not strictly necessary. However, keep in mind that due to the
specifics of MeTA1, the number of symbols that may be
exported for each stage is limited (see pmult-macros).
__preproc__ and __statedir__
built-in constant is slightly different from what it used to be in
5.0. These constants now refer to the current values of the
preprocessor command line and program state directory,
correspondingly. This should not affect your script, unless you
redefine the default values on run time. If your script needs to
access default values, use __defpreproc__ and
__defstatedir__, correspondingly (see Built-in constants).
The following example explains the difference between these:
$ cat pval.mf prog envfrom do echo "Default value: " __defstatedir__ echo "Current value: " __statedir__ done $ mailfromd --state-directory=/var/mfd --test pval.mf Default value: /usr/local/var/mailfromd Current value: /var/mfd
rate function,
you might consider using the new function rateok or
tbf_rate instead. For a detailed discussion of these functions,
see Sending Rate.
#pragma dbprop (see dbprop).
Mailfromd Manual:
This version of Mailfromd requires GNU mailutils version 2.0 or later.
Upgrading from version 4.4 to 5.0 requires no additional changes. The major differences between these two versions are summarized below:
getopt and varptr. See getopt.
verp_extract_user, sa_format_report_header,
sa_format_score.
The stack can be grown either by fixed size blocks, or exponentially. Upper limit can be specified. See stacksize.
Support for some deprecated features has been withdrawn. These are:
Mailfromd Manual:
The deprecated --domain command line option has been withdrawn. The short option -D now defines a preprocessor symbol (see Preprocessor Options).
This version correctly handles name clashes between constants and variables, which remained unnoticed in previous releases. See variable--constant shadowing, for a detailed description of it.
To minimize chances of name clashes, all symbolic exception codes has
been renamed by prefixing them with the ‘e_’, thus, e.g. divzero
became e_divzero, etc. The ioerr exception code is renamed to
e_io. See status.mf, for a full list of the new exception codes.
For consistency, the following most often used codes are available without
the ‘e_’ prefix: success, not_found, failure, temp_failure. This
makes most existing user scripts suitable for use with version 4.4
without any modification. If your script refers to any exception
codes other than these four, you can still use it by defining a
preprocessor symbol OLD_EXCEPTION_CODES, for example:
$ mailfromd -DOLD_EXCEPTION_CODES
Mailfromd Manual:
Upgrading from 4.2 to 4.3 or 4.3.1 does not require any changes to your configuration and scripts. The only notable change in these versions is the following:
The asynchronous syslog implementation was reported to malfunction
on some systems (notably on Solaris), so this release does not enable
it by default. The previous meaning of the --enable-syslog-async
configuration option is also restored. Use this option in order to
enable asynchronous syslog feature. To set default syslog
implementation, use DEFAULT_SYSLOG_ASYNC configuration variable
(see syslog-async).
The following deprecated features are removed:
#pragma option ehlo statement.
It became deprecated in version 4.0. See pragma-option-ehlo.
#pragma option mailfrom statement.
It became deprecated in version 4.0. See pragma-option-ehlo.
It became deprecated in version 3.1. See 30x-31x.
They are deprecated since version 4.0. See 31x-400.
Mailfromd Manual:
Upgrading to this version does not require any special efforts. You
can use your configuration files and filter scripts without any
changes. The only difference worth noticing is that starting from this
version mailfromd is always compiled with asynchronous
syslog implementation. The --enable-syslog-async
configuration file option is still available, but its meaning has
changed: it sets the default syslog implementation to use
(see syslog-async). Thus, it can be used the same way it was in
previous versions. You can also select the syslog implementation at
run time, see –syslog-async option, for
more detailed information.
Mailfromd Manual:
Upgrading to this version does not require any special efforts. You can use your configuration files and filter scripts without any changes. Notice only the following major differences between 4.1 and 4.0:
sprintf function
(see String formatting) and printf macro
(see printf).
retry, io-retry, and
connect-retry.
Mailfromd Manual:
Before building this version, please re-read the chapter See Building, especially the section Using non-blocking syslog.
Starting from the version 4.0, MFL no longer uses the predefined symbolic names for exception codes (previous versions used the ‘&’ prefix to dereference them). Instead, it relies on constants defined in the include file status.mfh (see status.mf).
However, the script files from 3.1 series will still work, but the following warning messages will be displayed:
Warning: obsolete constant form used: &failure Warning: remove leading '&' and include <status.mfh> Warning: Using built-in exception codes is deprecated Warning: Please include <status.mfh>
Another important difference is that pragmatic options ‘ehlo’
and ‘mailfromd’ are now deprecated, as well as their command line
equivalents --ehlo and --domain. These options
became superfluous after the introduction of mailfrom_address
and ehlo_domain built-in variables. For compatibility with the
previous versions, they are still supported by mailfromd
4.0, but a warning message is issued if they are used:
warning: `#pragma option ehlo' is deprecated, consider using `set ehlo_domain "domain.name"' instead
To update your startup scripts for the new version follow these steps:
#pragma option mailfrom value to
set mailfrom_address value. Refer to
mailfrom_address, for a detailed discussion of this variable.
#pragma option ehlo value to
set ehlo_domain value. Refer to
ehlo_domain, for a detailed discussion of this variable.
#include_once <status.mfh>
sed expression: ‘s/&\([a-z]\)/\1/g’.
hostname,
resolve, hasmx or ismx, add the following line
to the top of your script:
#require dns
See Modules, for a detailed description of the module system.
next with pass.
match_cidr, add the following line
to the top of your script:
#require match_cidr
See Modules, for a description of MFL module system.
Mailfromd Manual:
mailfromd binary no longer supports
--config-file (-c) option. To use an alternative
script file, give it as an argument, i.e. instead of:
$ mailfromd --config-file file.rc
write:
$ mailfromd file.rc
For backward compatibility, the old style invocation still works but
produces a warning message. However, if mailfromd
encounters the -c option it will print a diagnostic message
and exit immediately. This is because the semantics of this option
will change in the future releases.
prog helo
do
# Save the host name for further use
set helohost $s
done
Figure C.1: Implicit declaration, old style
has to be rewritten as follows:
set helohost ""
prog helo
do
# Save the host name for further use
set helohost $s
done
Figure C.2: Implicit declaration, new style
dbmap takes an
optional third argument indicating whether or not to count the
terminating null character in key (see dbmap). If your startup
script contained any calls to dbmap, change them as follows:
| in 3.0.x | in 3.1 |
|---|---|
| dbmap(db, key) | dbmap(db, key, 1) |
Mailfromd Manual:
Update your startup scripts and/or crontab entries. The
mailfromd binary is now installed in ${prefix}/sbin.
We also encourage you to update the startup script (run cp etc/rc.mailfromd /wherever-your-startup-lives), since the new version contains lots of enhancements.
Mailfromd Manual:
If you are upgrading from version 1.x to 2.0, you will have to do the following:
prog envfrom do … done
See Handlers, for more information about the prog statement.
rate statements, convert them to
function calls (see rate), using the
following scheme:
Old statement: if rate key limit / expr
New statement: if rate(key, interval("expr")) > limit
For example,
rate $f 180 / 1 hour 25 minutes
should become
rate($f, interval("1 hour 25 minutes")) > 180
mailfromd --compact --all
This is necessary since the format of mailfromd databases
has changed in version 2.0: the key field now includes the trailing
‘NUL’ character, which is also reflected in its length. This
allows for empty (zero-length) keys. See Database Maintenance, for
more information about the database compaction.
Mailfromd Manual:
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Mailfromd Manual:
This is a general index of all issues discussed in this manual
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https://www.gnu.org/software/adns
For more information about exceptions and their handling, please refer to Exceptions.
class ‘w’, see Sendmail Installation and Operation Guide, chapter 5.2.
class ‘R’
Sendmail (tm) Installation and Operation Guide, chapter 5.6, ‘O -- Set Option’.
When MFL has array data type, the second argument will change to array of strings.
There are two noteworthy exceptions:
require and from ... import statements, which must be
terminated with a period. See import.
Implementation note: actually, the references are not interpreted within the string, instead, each such string is split at compilation time into a series of concatenated atoms. Thus, our sample string will actually be compiled as:
$f . " last connected from " . last_ip . ";"
See Concatenation, for a description of this construct. You can easily see how various strings are interpreted by using --dump-tree option (see --dump-tree). In this case, it will produce:
CONCAT:
CONCAT:
CONCAT:
SYMBOL: f
CONSTANT: " last connected from "
VARIABLE last_ip (13)
CONSTANT: ";"
The subexpressions are numbered by the positions of their opening parentheses, left to right.
The subexpressions are numbered by the positions of their opening parentheses, left to right.
Notice that these are intended for educational purposes and do not necessarily coincide with the actual definitions of these functions in Mailfromd version 8.14.
The only exception is ‘not’, whose precedence in MFL is much lower than usual (in most programming languages it has the same precedence as unary ‘-’). This allows to write conditional expressions in more understandable manner. Consider the following condition:
if not x < 2 and y = 3
It is understood as “if x is not less than 2 and y equals 3”,
whereas with the usual precedence for ‘not’ it would have meant
“if negated x is less than 2 and y equals 3”.
This function is
part of the mailfromd library, See hasmx.
It is usually located in /usr/local/share/mailfromd/8.14/include/pp-setup.
This
is similar to GNU m4 --prefix-builtin options. This approach
was chosen to allow for using non-GNU m4 implementations as
well.
That is, if it supports Milter protocol 6 and
upper. Sendmail 8.14.0 and Postfix 2.6 and newer do. MeTA1 (via
pmult) does as well. See MTA Configuration, for more
details.
Support for other locales is planned for future versions.
For example:
prog header do echo unfold($2) done
Note, that the return code is inverted in respect to the system function ‘access(2)’.
It is made optional in order to provide backward compatibility with the releases of mailfromd prior to 5.0.93.
Although RFC 4408
introduces a special SPF record type for this purpose, it is
not yet widely used. As of version 8.14, MFL
does not support SPF DNS records.
https://tools.ietf.org/html/rfc4871
This will match most existing
installations. In the unlikely case that your $sysconfdir does
not end in /etc, you will have to edit the directive
accordingly.
The exact location is
determined at compile time: the /etc directory is the system
configuration directory set when building mailfromd
(see Building).
However, this is true only if the program
is exited the usual way (via QUIT or end-of-file). If it is
aborted with a signal like SIGINTR, the temporary directory is
not removed.
Depending on how mailfromd is
configured, ‘inet6’ may be not available.
https://www.rfc-editor.org/rfc/rfc1034#section-3.6.2
https://www.rfc-editor.org/rfc/rfc2181#section-10.1
This document was generated on August 13, 2022 using makeinfo.
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