SpamAssassin is a mail filter which attempts to identify spam using a variety of mechanisms including text analysis, Bayesian filtering, DNS blocklists, 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).
Windows Server 2008