Integrated into several varieties of MTA

Amavisd-new is a high-performance interface between mailer (message transfer agent - MTA) and one or more content checkers: virus scanners, and/or SpamAssassin. It is written entirely in Perl, assuring high reliability, portability and maintainability. It talks to MTA via (E)SMTP or LMTP, or by using helper programs. Best with Postfix, works with Exim, sendmail/milter or with any MTA as a SMTP relay. [http://www.ijs.si/software/amavisd/]

MailScanner now includes support for SpamAssassin. This is "a virus scanner for e-mail designed for use on e-mail gateways. It can also detect a large proportion of unsolicited commercial e-mail (spam) passing through it." MailScanner does an excellent job with file names and types, and can be set to quarantine encrypted .ZIP files and apply normal filename rules and virus scanning inside unencrypted ones.
[http://www.sng.ecs.soton.ac.uk/mailscanner/]

Another option is to use a filtering SMTP proxy such as spampd. It is typically used to filter the mail between an external-facing MTA instance/relay, and an "internal" MTA instance.
[http://www.worlddesign.com/index.cfm/rd/mta/spampd.htm]

Integrated into Sendmail

With Sendmail, Spamassassin can be called for every user by editing /etc/procmailrc . More details at http://www.stearns.org/doc/spamassassin-setup.current.html#sitewide

An alternative is to use the smtp-vilter high-performance content filter using the sendmail milter API which has a backend for Spamassassins spamd. More details at http://www.msys.ch/products/software/unix/sendmail/smtp-vilter/

MIMEDefang, a sendmail milter written by Roaring Penguin Software, filters all e-mail messages sent via SMTP through a sendmail installation, blocking common mail viruses, and now – with the help of SpamAssassin – spam. "You can use SpamAssassin to test for spam, and then all of the MIMEDefang goodies to reject, manipulate or otherwise mangle the message." Integrated with the MTA to the level of returning 5xx error codes during the SMTP session, so viruses or detected spam can be rejected at the delivery, which notifies the sender, that the mail was rejected, without generating an additional email message.[http://www.roaringpenguin.com/mimedefang/]

spamass-milt [http://savannah.gnu.org/projects/spamass-milt/] is a sendmail milter by Georg C. F. Greve, which allows sendmail users to filter spam at the heart of the sendmail message pipeline. It also allows SpamAssassin to be used for UUCP sites. If you plan to use this, be sure to read Kevin [McGrail]'s walkthrough at Peregrine Hardware. [http://www.peregrinehw.com/downloads/SpamAssassin/INSTALL-spamassmilter].

milter-spamd [http://www.benzedrine.cx/milter-spamd.html] is a simple BSD-licensed sendmail milter by Daniel Hartmeier.

BSM Development have released [MailCorral] and SpamCorral for use on UNIX and Linux systems, mail/spam filtering software using the sendmail milter interface.
[http://www.bsmdevelopment.com/]

Yet Another Sendmail-SpamAssassin Interface Milter, milter-spamc by Snert [http://www.snert.com/Software/milter-spamc/index.shtml]

Integrated into Postfix

The easiest way to integrate postfix and spamassassin is to use spamd. See IntegratedSpamdInPostfix.

Alternatively, a more complex scheme is to integrate it using Amavis, as described in IntegratedInPostfixWithAmavis.

Integrated into Qmail

SpamAssassin can be integrated into qmail system-wide using qmail-scanner, described in IntegratedInQmailWithQmailScanner.

Since qmail allows users to configure their own delivery options via ~/.qmail files, an alternative option, if you have spamd running and only want to scan mail delivered to local users, is to use ifspamh: see IntegratedInQmailWithIfspamh.

Integrated into Exim

SpamAssassin can be integrated into [http://www.exim.org/ Exim] in three ways:

1. As an [http://duncanthrax.net/exiscan-acl/ Exiscan]-extended ACL condition stack, Exim can reject spam after reading the body, but before Exim acknowledges acceptance of the email. [http://www.debian.org/ Debian Linux]'s exim4-daemon-heavy comes with the exiscan patch built in. You can discover its presence in your distro's exim binary directly with the command exim -bV or exim4 -bV; look for the phrase Contains exiscan-acl patch.
   

2. As an Exim 4.x loadable module or local_scan.c replacement. [http://marc.merlins.org/linux/exim/sa.html SA-Exim] also allows SpamAssassin to reject spam before its accepted by your MTA. More info at [http://www.timj.co.uk/linux/exim.php].
   

3. As an [http://dman13.dyndns.org/~dman/config_docs/exim-spamassassin/ Exim transport].
   
   

Integrated into Courier-MTA

If you use the Courier MTA, you can use maildrop, described in IntegratedInCourierUsingMaildrop.

There is also a rudimentary HOWTO at [http://forums.gentoo.org/viewtopic.php?t=28392 the Gentoo forums] for integrating SpamAssassin and f-prot with Courier-MTA.

There is another HOWTO at [http://da.andaka.org/Doku/imapspamfilter.html] to feed SpamAssassin's bayes filter via Courier-IMAP.

Integrated into CommuniGate Pro

CGPSA external filter: http://www.tffenterprises.com/cgpsa/

CGPAV external filter: http://program.farit.ru/doc/cgpav.html

SpamAssassin plugin for CommuniGate Pro 4.x

Installation and usage instructions can be found at
http://www.stalker.com/CGPSpamCatcher/#Integrate

ftp://ftp.vsu.ru/pub/apps/CGatePro/sa-cgp.c
ftp://ftp.vsu.ru/pub/apps/CGatePro/Mail-SpamAssassin-2.63-ai.diff (required)

Build:
AIX: cc_r sa-cgp.c libspamc.c utils.c -o sa-cgp
Solaris: cc -mt sa-cgp.c libspamc.c utils.c -o sa-cgp -lsocket -lnsl

Integrated into XMail (Unix)

SpamAssassin Filter (sa_filter.pl) is an [http://www.xmailserver.org/ XMail] filter send incoming email messages to SpamAssassin for spam filtering.

sa_filter.pl calls spamc, the SpamAssassin client (spamc calls spamd) and passes the output of spamc back to XMail for delivery. Neither sa_filter.pl nor spamc will delete emails that are flagged as spam.

Please find the filter source code and documentation at [http://www.drakeconsult.com/xmail/ Drake Consulting]

Integrated into Exchange (Windows)

See: http://www.christopherlewis.com/ExchangeSpamAssassin.htm

Integrated into Novell Netmail

[http://netmail.sourceforge.net/ Novell NetMail Agent]

Notes for MTA-Integration Developers

See MtaIntegrationDevNotes.