T. Eggendorfer (Germany)
Spam, Tar Pit Simulator, spamd, SMTP tar pit
OpenBSD's spamd implements a combined greylisting and SMTP tar pit to thwart spammers. To unknown senders, OpenBSD's spamd behaves like a tar pit, ending with a temporary error condition as any greylister would do. If a greylisted sender reconnects, it is then added to a white list and allowed to connect to the MTA. A blacklisted connection will be send to a SMTP tar pit. By contrast, the SMTP tar pit simulator simulates a SMTP tar pit's behaviour for a certain period of a connection and then speeds up the connection. Recent tests show, that both the tar pit simulator and greylisting are able to reduce incoming spam to 20% of its original value. However, from a technical point of view, both systems work differently and have their specific advantages and disadvantages. This paper describes how both technologies work and discusses their pros and cons.
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