JAM Software released a Windows version of SpamAssassin, a powerful anti-spam solution that works in conjunction with MTA software like MS Exchange or Hamster.

One of the standout features of SpamAssassin is its ability to analyze text using advanced algorithms such as Bayesian filtering and DNS blocklists. This means that the software is able to identify and block spam messages before they even reach your inbox.
Another great feature of SpamAssassin is its collaborative filtering database, which allows users to share information about spam messages in real-time. This helps to keep the software up-to-date and ensures that it remains effective against even the most advanced spam attacks.
For Windows users, SpamAssassin has been adapted by JAM Software and includes several modules, including spamassassin.exe (mail filter), spamd.exe (daemonized version of SpamAssassin), WinSpamC.exe (client for spamd), sa-update.exe (SpamAssassin rule updates), and sa-learn.exe (trains bayes filter with spam/ham mail).
Overall, if you're serious about protecting your email account from spam, then SpamAssassin is definitely a software worth considering. Its advanced features and the fact that it's continually updated by the Apache Software Foundation make it an extremely powerful anti-spam solution.
Version 3.4.1:
* Native 64 bit support has been integrated
* SpamAssassin version 3.4.1 integrated
* ActivePerl 5.8 replaced by Strawberry Perl 5.22
* Support for Windows XP and Server 2003 dropped
* critical error in DNS-based spam tests removed
* A few minor fixes have been incorporated.