Tagged Message Delivery Agent (TMDA) is designed to significantly reduce the
amount of spam (junk-mail) you receive.  TMDA strives to be more effective,
yet less time-consuming than traditional spam filters.

The technical countermeasures used by TMDA to thwart spam include:
- whitelists: accept mail from known, trusted senders
- blacklists: refuse mail from undesired senders
- challenge/response: allows unknown senders which aren't on the whitelist or
  blacklist the chance to confirm that their message is legitimate (non-spam)
- tagged addresses: special-purpose e-mail addresses such as time-dependent
  addresses, or addresses which only accept certain kinds of communication.
  These increase the transparency of TMDA for unknown senders by allowing them
  to safely circumvent the challenge/response system.

TMDA can also be used as a general purpose local mail delivery agent to filter,
sort, deliver and dispose of incoming mail.

WWW: http://tmda.net/