On Mon, 05 Jan 2004 04:28:26 +0900, itojun(_at_)itojun(_dot_)org (Jun-ichiro
itojun Hagino) said:
there seem to be many interesting discussions on secondary MX and spam
relays. basically, secondary MXes normally do not check the existence
of accounts (like foo(_at_)itojun(_dot_)org) and it will get queued,
while primary
MX can reject it at instant. this may be ASRG topic, but i guess
there's something to be done in SMTP level.
The only reason this is done by the spammers at all is because often in
these situations, the primary MX will blindly accept mail from the secondary
without applying anti-spam controls. Certainly, such broken sites are in
the minority - but when 80% of your attempts get blocked, finding a loophole
that exists even in 2-3% of sites means an 10% efficiency gain....
I can't recommend any change in SMTP to counter this - the same sites that
have the problem are the same sites that are unlikely to deploy any changes to
fix the problem.
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