Tagged Message Delivery Agent
TMDA is a challenge/response system that has a number of interesting features, some of which include:
Optional auto-whitelisting of senders
A web interface (separately available from http://tmda.net/tmda-cgi/)
Responds “smartly” to automated messages from mailing lists, etc.
Support for client-side From: address generation for “mangled” addresses
Although the focus of TMDA appears to be qmail, TMDA has good support for other MTAs as well, including the two we cover in this book (Postfix and Sendmail) and Exim. TMDA has whitelisting and blacklisting support, as every challenge/response system must have. TMDA utilizes the Hashed Method Authentication Codes (HMAC) defined by RFC2104, which are encoded in the To: line ...