SpamAssassin for Windows

From JAM Software:

SpamAssassin is a mail filter which attempts to identify spam using a variety of mechanisms including text analysis, Bayesian filtering, DNS blacklists, and collaborative filtering databases. SpamAssassin is a project of the Apache Software Foundation (ASF). SpamAssassin was adapted for Windows by JAM Software. In combination with a MTA (e.g. Hamster or MS Exchange) it's a very powerful anti-spam solution. The freeware contains, beside several modules, the following SpamAssassin components as executable files for Windows (.exe): spamassassin.exe (mail filter), spamd.exe (daemonized version of SpamAssassin), WinSpamC.exe (client for spamd), sa-update.exe (SpamAssassin rule updates), sa-learn.exe (trains bayes filter with spam/ham mail).