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How do I use SpamAssassin with procmail to forward mail and to Bayes training?

This procmail script is designed for people who have their mail forwarded through a server (e.g, example.com) but then read their mail on a non-publicized account on a different server (e.g., privateaddress@example.net). This is quite common for folks who have a vanity domain name but then read their mail through an office Exchange server, home DSL email account, etc.

The idea is for procmail on the first server to run each message through SpamAssassin, and then forward the message on to the private address.

The trick for Bayes training is to add some extra procmail rules to specify special processing for training messages. The following is based on having a catchall address for all mail sent to example.com, so I can trigger the bayes training by sending mail to spam@example.com and ham@example.com. It is left as an exercise for the reader to create an alternative script that triggers based on a passphrase added to the subject, and uses formail to remove that passphrase before passing the message to sa-learn.

Note that this setup still only works passably with Outlook and Exchange, because even resending the message causes a new Message-ID header to be created and the old Received headers to be lost. Other headers are still carried over. To trigger Bayes learning from Outlook on false negatives, choose Action: Resend this Message (you have to remove any From and CC headings and change the To field to spam@example.com). Note that nearly every other mailer (except for AOL) supports real redirects; see [http://www.stearns.org/doc/spamassassin-setup.current.html#redirect].

Note that after logging into the server, you can find the path for spamassassin by typing which spamassassin.

#Uncomment the following lines and use tail -f procmail.log to debug
#LOGFILE=$HOME/procmail.log
#VERBOSE=yes
#LOGABSTRACT=all

# Feed redirected spam to sa-learn

:0
* ^To:.*spam@example.com
* < 256000

   {
   :0c: spamassassin.spamlock
   | sa-learn --spam

   :0
   mail/spam
   }

# Send all other mail through SpamAssassin

:0fw: spamassassin.lock
* < 256000
| /usr/bin/spamassassin


# Mail that is very likely spam (>10) can be saved on the server
# (not forwarded), of by moving the # down one line, even dropped
# on the floor.  Note that dropping mail on the floor is a *bad*
# idea unless you really, really believe no false positives will
# have a score great than 10.  If you want all mail forwarded,
# just add #'s in front of each of these lines:

:0
* ^X-Spam-Level: \*\*\*\*\*\*\*\*\*\*
#/dev/null
mail/tenplusspam


:0 # All spam with a score less than 10
! privateaddress@example.net # Forward mail to my non-publicized address
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