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Killing Spam with Greylisting

At our November, 2004 meeting, Barb Dijker of Netrack presented the latest tools in the constant battle against spam, greylisting.

Greylisting ( takes advantage of the fact that most spam delivery engines don't queue mail if it is not immediately deliverable. When greylisting is integrated into a Mail Transfer Agent (MTA), it gives the initial connection with an unknown server an SMTP temporary failure notification. If that same server attempts to re-try the mail delivery at a later time, the mail is accepted and the server is added to a greylist.

Barb talked about details of how she has greylisting configured at Netrack, and some of the countermeasures that spammers are already taking to fight this technology. She also discussed the Sender Policy Framework (SPF) and how people are beginnning to use SPF to denote valid outbound e-mail servers for a particular domain.

There was also audience discussion of various DNS-based blacklists, and one item of note is that Spamhaus ( now has a blacklist option that not only attempts to block the big spammers' e-mail, but also includes two other blacklists, CBL that attempts to track compromised machines (like home PCs) that could be used as spam relays, and OPM, the open proxy monitor.

Barb's slides are available in the FRUUG meeting archive (PDF, 420K).

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February 15, 2009

February 2008: FRUUG Enters Quiescent Phase
After 27 years running, we're suspending operations.

Future Meetings:
None planned

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