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What is procmail?
Procmail is a mail filtering program. It allows to redirect mail from certain addresses or containing suspicious Subject headers directly to the garbage.
Configuring procmail.
To setup procmail you need to create 2 files in your home directory.
The first file ".forward" contains the line
and has the effect that your mail will be piped through the procmail filter. On a Linux box, you don't need to have a .forward file and the program procmail is at a different place.
The second file ".procmailrc" contains the filtering data. The following example of a .procmailrc file:
* ^From.**

* ^Subject: .*xxxx

discards all mail from and sends all mail containing "xxxx" in the subject to the garbage. It then sends a copy of the mail to the address
A word of advise
Be on the safe side with filtering your mail. You might filter away mail you actually wanted to see. You can change the Unix garbage "/dev/null" in the above filter to a file in your home directory and empty this from time to time.

Simplicity, Clarity, Generality B.W. Kernighan, R. Pike, in "The Practice of Programming".