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At our November, 2004 meeting, Barb Dijker of Netrack presented the latest tools in the constant battle
against spam, greylisting.
Greylisting (greylisting.org)
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
(www.spamhaus.org)
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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