Freeware: Spamassassin

SpamAware 4.6Spam filter&Antivirus (ClamAV) plugin for Outlook&Outlook Express. It uses spamassassin to score new incomming mails and decides based on the settings made in options what to do with the mail. It supports Black- and Whitelist filtering and Bayes.

SpamAssassin 3.0\Server side spam email blocker. 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 for Windows 1.1 spamassassin was ported for Windows by JAM Software. In combination with an MTA (e.g. Hamster or MS Exchange) it's a very powerful anti-spam solution.

No Spam Today! for Servers Freeware 3.0.5.1Mail spam filter (SMTP/POP3) that easily integrates with every mail server software. NoSpamToday! includes the award-winning spamassassin filter, an attachment blocker, and an RBL filter. Virus scanners can be integrated into the filtering pipeline.

VirusCop 2.00VirusCop is a simple freeware Windows program for reporting virus spam, erroneous e-mail bounces and other spam. VirusCop can automatically find email complaint contacts and automatically report spam in bulk.

No Spam Today! SMTP Proxy Free 2.0.4.4No Spam Today! is an SMTP proxy server based spam filter that sits between the internet and your mail server. Incoming mail is accepted from the open internet, checked for spam, and is then delivered to your existing SMTP mail server. NoSpamToday!

eWall SMTP Proxy 4.0eWall is a gateway between the Internet and your mail server. It monitors the SMTP traffic in real-time, catching the majority of spam and viruses. The chain of flexible PHP filters stops more than 95% of unwanted emails out of the box.