Mailfilt is a perl script that filters incoming mail based upon a set of rules defined in a /.rules/ file. The location of that file and the mail directory in which to put messages are specified at the beginning of Mailfilt itself. The default directory is "$HOME/mail".

The /.rules/ file has a very rich syntax but is formatted like a makefile. The following shows a sample /.rules/ file that illustrates many of the features:

PGP

Mailfilt has built-in support for PGP signatures. When it encounters a PGP signed message, it will attempt to run /pgp/ to authenticate the message. For this to work properly, pgp must be in one of the directories in the PATH statement in the configuration section of the Mailfilt code and your public keyring must be in the directory pointed to by the PGPPATH statement.

The signature block will appear in the message as it was sent, but following the END SIGNATURE marker, a couple lines will be inserted showing whether /pgp/ could authenticate the message.

Users without pgp can use mailfilt without problem, except that an error message will appear in the logfile each time a signed message is received.

Example .rules file:

/dev/null:
    Subject: this is junk

jimbob@the.farm:        #Forward this stuff to Jim Bob
    Subject: Farm report
    &!From: jimbob

|/usr/bin/handle-cronmail:
    From: root
    &Subject: ^cron                #Subject must start with cron

bulk:
    Rcpt: biglist@alma.matter #biglist must be in To: or Cc:

personal:         #Stuff addressed to either of my mail aliases
    To: myname@big.fast.computer
    
    To: myothername@big.fast.computer

primary:        #Anything that hasn't already matched will go to this file

In this example, mail with "this is junk" in the subject will go to "/dev/null". Mail with "Farm report" in the subject that doesn't come from /jimbob/ will be mailed to /"jimbob@the.farm"/. Mail from /root/ with /cron/ in the subject line will be put in the file /bulk/ in the mail directory. Mail that has /biglist@alma.matter/ in the To: or Cc: lines will also be put in /bulk/. Anything that hasn't met the above criteria and that has /myname@big.fast.computer/ in the To: line will be put in the file /personal/ in the mail directory. Finally, everything else will be put in the file /primary/. This means that nothing will end up in "/var/spool/mail".

Some general rules to remember

The first rule that matches is the one used.
Mail will only be forwarded once (to prevent looping)
Searches are in regex format (substring unless special operators given)
All matches are case-insensitive
Rcpt: is the combination of To: and Cc:
Filenames are in the mail directory unless they begin with a slash
If a message doesn't match any rules, it will be placed in /var/spool/mail
Logical ORs are accomplished using multiple sets of criteria under a single destination---see the "personal" block in the example above.

Grammer for .rules file:

FILE       ::=        {SET}

SET        ::=        TARGET: {COMMENT} \n
                      {RULESET}
                      {SET}

TARGET     ::=        FOLDER | ADDRESS | PIPE

RULESET    ::=        WS RULE
                      WS ANDRULE
                      {SKIPLINE RULESET}

ANDRULE    ::=        &RULE {ANDRULE}

RULE       ::=        [!]HEADER: WS regex {COMMENT} \n

HEADER     ::=        From | Subject | To | Rcpt | Date | ....

ADDRESS    ::=        user@machine

FOLDER     ::=        filename
           |          /path/to/file

PIPE       ::=        |/path/to/program

SKIPLINE   ::=        \n{COMMENT}\n

WS         ::=         \t  {WS} 
           |          ` ' {WS}

COMMENT    ::=        {WS}#string

Verision History

New Features in Version 1.3

Bug fix: Pipe headers couldn't have whitespace

New Features in Version 1.21

Bug fix: Headers spanning multiple lines were truncated
Bug fix: cc header not included in Rcpt

New Features in Version 1.20

PGP support
Header matches are now case-insensitive

New Features in Version 1.11

Better file locking for use with sendmail and mail agents
Can save messages to pipes
This page updated slightly

mfisk/mailfilt

PGP