Barry Shein <bzs(_at_)world(_dot_)std(_dot_)com> wrote:
There's also Jef Poskanzer's greymilter which basically requires one
re-send from each never before seen mail server not in a white list.
And sendmail (and others') HELO delay (delay sending HELO a short
period of time) and don't speak until you're spoken to whatever they
call it (I use it, the sender must wait for the SMTP responses, can't
just dump an SMTP conversation at you.)
They're basically isomorphic to hashcash type solutions, increase the
sender's cost, but very transparent and quite clever because of that.
They have nothing to do with increasing the sender's cost. Rather,
they take advantage of the fact that legitimate mailers implement the
RFCs in ways that spamware typically doesn't, so they test for that
and spamware flunks.
Seth
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