Open Source mail filter, written in Perl, to identify spam using a wide range of heuristic tests on mail headers and body text. Free software. Can be used as a standalone mail filter, or from procmail. Site includes download, news, FAQ, and documentation.

Book by Alan Schwartz. Description, reviews, table of contents, and short preview texts.

Bug-tracking system for the SpamAssassin mail filtering project.

User contributed documentation, testimonials, tricks and tips for the mail filtering software.

Encyclopedia article about the mail filtering software, including history and details of the various techniques employed.