Dr. Tom's Simple Introduction to Procmail

What is Procmail? Procmail is an email filter that runs under the Unix operating system. It is very powerful.

What is this page? This is a simple and practical introduction for beginners. My intent is to answer basic questions about how procmail works and how to use it first before you get flooded with details about the powerful things that can be done with it. I assume you have a basic knowledge of Unix.

How does it work? The basic scheme:

1. Email arrives at your computer.
2. The mail agent looks for a ~/.forward file, which is a file in your home directory. It can be used to send your email on to another computer. It is an automatic forwarding mechanism.

   If you are not familiar with the notation, a "~" signifies your home directory. Starting a file with "." means that is not normally visible using the ls program. However, you can see such files by using the -a flag: ls -a ~/.forward

3. An example ~/.forward file for calling procmail is:

   "|IFS=' ' && exec /usr/local/bin/procmail -f- || exit 75 #toms"
   

   This tells the mail agent that when email arrives it should execute the procmail program. (See the unix manual page for 'forward' for information about how this works.)
4. Procmail reads your ~/.procmailrc file to figure out what to do with the new email.
5. Here is an example ~/.procmailrc file. Lines that begin with # are comments.

   # version = 1.07 of .procmailrc 2003 Aug 26
   # this is a ~/.procmailrc file
   #
   # For information about this file, see
   # https://alum.mit.edu/www/toms/procmail.html
   #
   # www.procmail.com
   #
   # General questions:
   # http://www.uwasa.fi/~ts/info/proctips.html
   #
   # man page:
   # http://mirrors.ccs.neu.edu/cgi-bin/unixhelp/man-cgi?procmailrc
   # **********************************************************
   
   # Preliminary setup
   
   # http://pm-doc.sourceforge.net/pm-tips-body.html#always_set_shell
   SHELL = /bin/sh
   
   # This part tells procmail the locations of various files.
   # You will need to change these to fit your system!
   # Please check if all the paths in PATH are reachable,
   # remove the ones that are not.
   
   PATH=$HOME/bin:/usr/bin:/usr/ucb:/bin:/usr/local/bin:/opt/sfw/bin:.
   MAILDIR=$HOME/Mail      # You'd better make sure it exists
   DEFAULT=/var/mail/toms
   LOGFILE=$MAILDIR/from
   LOCKFILE=$HOME/.lockmail
   
   # **********************************************************
   # Controls for what to do with various kinds of email follow:
   
   # Stop listening to that stupid Joker
   :0 B
   * Choose a Prank from the list below
   Joker.junk
   
   

6. Note all the preliminary stuff. It tells procmail that it should use the sh shell (as recommended), and where various files and directories are.
7. An instruction starts with ":0"
8. The "B" after the ":0" means to look in the body of the email. See the procmailrc manual page for details.
9. A rule starts with "*". This rule is the string "Choose a Prank from the list below".
10. If that string is found in the body of the email, then the email will be sent to your $HOME/Mail/Joke.junk file. $HOME is an environmental variable that defines where your home directory is. In shells you could use "~" (see above) but procmail doesn't know how to do that so use $HOME instead.
11. You can send an email anywhere. If you send it to /dev/null, it will never be seen since that is the Unix bit bucket! I wouldn't suggest doing this until you are confident about how this program works ...
12. You can have multiple rules.

Links

• Home page procmail. This is useless if you are a beginner!
• Procmail Documentation Project. You would think otherwise from its title but this too is useless if you are a beginner!
• Timo's procmail tips and recipes. Good but overwhelming.
• Foiling Spam with an Email Password System I found this more useful than anything else because it is straightforward and practical!
• Manual pages dead links!
  • procmailrc manual page. For configuring the .procmailrc file - Highly useful!
  • procmailsc manual page. For undertanding scoring.
  • procmailex manual page. Examples
• PROCMAIL QUICK START
  • Filtering Mail FAQ. Pretty ancient, seems to be out of date
  • mirrors
  • faq at www.ii.com
• Other useful procmail links
  • using metamail with procmail
  • using spamassasan with procmail