"Spam has become a real problem these days. The more people who
know your e-mail address, the more unwanted pieces of mail you
receive. If you used your e-mail to register on some Web sites or
publish a few articles in the newsgroup, you probably started to
receive more unwanted messages than welcome ones. Fortunately, the
users of Linux and other open-source systems have written a lot of
good anti-spam filters. You can find dozens of these programs on
GNU.org and Freshmeat. The anti-spam software may be sophisticated
or simple, easy or difficult to use, more or less effective. Amidst
the larger well-known projects, there is SpamAssassin, written by
Justin Mason, and bogofilter, a Bayesian filter written by Eric S.
Raymond, and others.
"Testmail, the filter discussed in this article, is a Perl
filter of average size and moderate complexity. It checks e-mail
messages available at the POP3 server, filters them according to
defined rules and, depending on the selected method, sends messages
to the local mailbox or removes them from the server. Testmail
requires the Perl libnet, Net-Ping and Socket modules..."