tkbiff allows arbitrary commands to be executed upon mail reception. If you like programs such as xbiff and xbiff++ but wish they were more flexible, then you'll like tkbiff. Unlike other biffs, tkbiff is fully customizable. tkbiff also doesn't waste your valuable screen space with icons; instead, it shows you the mail itself. It supports UNIX, Mac, and Windows, IMAP, POP, and UNIX-style mail files, and SSL and APOP.
MailStripper Pro is a mail scanner that aims to remove spam and viruses from incoming mail. It recognises and decodes many obfuscation techniques used by spammers and uses several different mechanisms to recognise spam which are immune to Bayes poisoning, and has achieved real-world success of over 99.8%. It is MTA-independent and does not implant itself into your mail server. Instead, it functions as a proxy, allowing the MTA to reside on a different server.
TkRat is a graphical Mail User Agent (MUA) which handles MIME. It is mainly written in C, but the user interface is done in Tcl/Tk. The program currently understands UNIX mailboxes, POP, IMAP, and mh folders. Messages are sent via SMTP or any user configured program (sendmail, for example). It has support for disconnected IMAP operations.
Maverix is an AOLserver module that implements the SMTP protocol and acts as an SMTP proxy with anti-spam and anti-virus capabilities. It includes a Web interface to manage quarantined messages and an administrative interface based on OSSWEB. Supported anti-spam software includes SpamAssassin and DSPAM, and supported anti-virus software packages are ClamAV and Sophos. Features include whitelisting, greylisting, and blacklisting, periodic digests with quarantined messages, a challenge/response mechanism, POP-auth, and short-TTL URLs for digests.