Phalanx

Phalanx is a powerful spam filer application for POP3 accounts. It can be used with any mail client. Phalanx supports APOP (MD5) and secures connections (SSL) for authentication on the mail server. It classifies messages from specific senders as ham or spam. With rule sets you can create own rule files, that can be included in Phalanx. External rule files (rule sets) are much moor powerful and flexible. Phalanx can be extended with plug-ins. Plug-ins can filter messages with complex methods.

Requirements:

Microsoft .NET Framework 2.0