On 12/13/2012 09:16 AM, Barry Shein 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.
Given botnets, anything that tries to shift burden back onto the
sender is not very likely to be effective in the long run. Yes, you
might get some short term relief, but the firehose is just a software
update away.
Mike
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