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Greylisting usefulness (was Re: SMTP Transferred-By-Reference)

2007-11-12 12:34:18

Dave Crocker wrote:

Graylisting is generally acknowledged to have current tactical utility
but something that spammers will adapt to whenever they feel the need.

Actually, I think greylisting will have longer-term uses than that.
Forcing spammers to be pinned to the same IP address for a while gives
techniques like DNS-based blocklists time to catch up.  So while it's
trivial to adapt to greylisting, it makes your zombie machine more
likely to be recognized as such during the retransmission.  I think
the OP had a good point about being able to make better decisions in
non-realtime, but I think his mechanism for deferring the decision is
seriously flawed.