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.

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

Bug-tracking system for the SpamAssassin mail filtering project.

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

A community-maintained collection of custom rules for SpamAssassin.

Update server hosted by OpenProject, including the recommended rules from the SpamAssassin Rules Emporium. Includes usage instructions.

Article by Christopher Lewis, describing how to implement SA mail filtering with MS Exchange using a custom Event Sink. Includes source code and installation program to download.

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

Online edition of a book by Alistair McDonald. Includes chapter summaries, and the full text from two chapters.