A tarpit, or teergrube (German for tarpit) is basically an extremely slow SMTP server. The thinking behind this is that most MTAs allow some method of distinguising "normal" email from SPAM, and if the email is deemed to be SPAM it would be rude not to accept it.

In this case though we accept the mail very slowly, in fact it is possible to maintain an SMTP session for more than a day. If enough of a spammers connections are slowed then it may become unviable for the spammer to continue in business (shame!). It may also be possible to catch a spammer in the act, allowing the admin of the server that is being used (be it an open proxy or a dialup account) to further trace the culprit.

The domain teergrube.org was registered for a little open source project, a portable, configurable tarpit. Progress has been slow, the first release is half written in Perl, and there is NO firm release date (I find far better uses for my "copious free time"™).