Since I last announced it here, I've improved my Tagged Message Delivery Agent, making it much easier for legitimate, but unknown senders to get mail through to you. It now validates these messages using a simple challenge/response process similar to SpamCop's.
TMDA is an OSI certified Python application for qmail systems designed to significantly reduce the amount of SPAM/UCE you receive. A "whitelist" filter allows known contacts immediately into your mailbox, and all others must reply to a simple confirmation to validate their message. Once they respond to the confirmation, their original message is delivered to you.
For more information including download locations and installation instructions, visit the TMDA homepage:
Jason R. Mastaler
<P><A HREF="http://tmda.sourceforge.net/">TMDA 0.37</A> - SPAM reduction system for qmail. (20-Sep-2001)