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Tagged Message Delivery Agent (TMDA)


TMDA is an open source software application designed to significantly reduce the amount of spam (Internet junk-mail) you receive. TMDA strives to be more effective, yet less time-consuming than traditional spam filters. TMDA can also be used as a general purpose local mail delivery agent to filter, sort, deliver and dispose of incoming mail.

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.
This combination was chosen based on the following assumptions about the current state of spam on the Internet:
  1. You cannot keep your email address secret from spammers.

  2. Content-based filters can't distinguish spam from legitimate mail with sufficient accuracy.

  3. To maintain economies of scale, bulk-mailing is generally:
    • An impersonal process where the recipient is not distinguished.
    • A one-way communication channel (from spammer to victim).

  4. spam will not cease until it becomes prohibitively expensive for spammers to operate.