From: Daniel Feenberg <feenberg(_at_)nber(_dot_)org>
....
Yes, but some spammers do not control the relevant MTA, as for example if
it is an open relay. Teergrubing must have very strong incentive effects
on open relays if it becomes reasonably widespread. And this incentive
applies even if the relay has no legitimate mail to transfer to the
victim.
I'm sorry but that's standard anti-spammer self-contradictory wishful
thinking. Open relays are ill maintained machines. Well maintained
machines don't need any incentives from teergrubers to be fixed after
being attacked by spammers as open relays. Badly maintained machines
don't have anyone who might notice the effects of teergrubing.
The biggest reason that teergrubing is silly is that there always have
been and always will be more unintentional teergrubing machines than
can ever be installed intentionally. Anyone who runs a non-trivial
bulk mail operation such as a mailing list knows too well that a
significant fraction of legitimate SMTP servers stall for longer than
typically recommended teergrubing durations. It doesn't matter whether
they stall because the 3 or more DNS lookups required by an SMTP server
to receive a message can teach take 90 seconds or a total of more than
5 minutes, because some spam filters need 5 minutes to get an answer,
or the many other reasons that can stall STMP. Whatever the reason,
they look the same to all bulk mailers as the trivial number of
intentional teergrubers. That's why all useful MTA client code has
timeouts to defeat teergrubers.
Vernon Schryver vjs(_at_)rhyolite(_dot_)com
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