8/11/2006; 2:33:20 AM

TMDA ... an anti-spam solution ...
Several years ago, while at Novell, I began work on a simple idea that I called AgreeMail. It never went anywhere, however it was an anti-spam solution based on an idea that I got at a Foresight Institute conference.

The idea was pretty simple. For any e-mail that was sent to me, the AgreeMail engine would check to see if it came from an "approved" sender. If it wasn't, then it would automatically kick back an e-mail to the sender with an "agreement" that had to be replied to. When the AgreeMail engine received the "agreement" it would add the person to the approved list and let their e-mail through.

Well ... years later ... here is the solution as an Open Source project! I am now updating my mail server, and will soon be installing the TMDA engine.

This article is a great overview of TMDA, and the benefits!

TMDA Ends Spam. Tagged Message Delivery Agent (TMDA) is a challenge/response style anti-spam system which I've been using successfully for about six months. The system is based on a white list. When someone not on the list sends me a message, their message is held in a queue, and a challenge is emailed back to them. When they respond to the message, they're added to my white list, and their original message is delivered to me. I've seen some resistance to systems like TMDA. This resistance comes in two basic objections: (1) it doesn't work, and (2) it's too rude. These objections are based on encounters with systems with various obvious faults, but condemning all challenge/response systems based on some bad implementations is like saying that cars are a bad idea because the Model A Ford has some problems. I intend to show that TMDA works well and that the real debate is over whether a system like it makes victims out of the people who aren't using it. [kuro5hin.org]