milter-greylist -- GreyList milter for sendmail<hr>
<a href="http://hcpnet.free.fr/milter-greylist/">http://hcpnet.free.fr/milter-greylist/</a><hr>
milter-greylist is a stand-alone milter written in C that implements
the greylist filtering method, as proposed by Evan Harris.

Grey listing works by assuming that unlike legitimate MTA, spam engines
will not retry sending their junk mail on a temporary error. The filter
will always temporarily reject mail on a first attempt, and to accept
it after some time has elapsed.

If spammers ever try to resend rejected messages, we can assume they will
not stay idle between the two sends (if they do, the spam problem would
just be solved). Odds are good that the spammer will send a mail to an
honey pot address and get blacklisted in several real-time distributed
black list before the second attempt.
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