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Re: Requiring PTR

2008-04-12 11:51:23

Hector Santos wrote:
Many systems, and naively believed AOL too, I believe used services like from MAPS RBL which lookup the zone owner to determine if this was a home or business tier.

They do -- or rather, dynamic vs. static. If you're in the MAPS dynamic IP range, you won't even get a TCP connection; you'll be blocked at the firewall.

Its stupid I think and x821 always allowed PTR checking as an option, but it was so unreliable, it wasn't a real issue and hardly used in my experience.

AOL has been checking for a valid PTR for at least five years. It was their judgment that a lack of PTR record was a reliable indicator of a spam source. They also experimented with verifying that the PTR and the forward A record match, but that got way too many false positives.

FWIW, I ran a bunch of tests using our traps and a pretty good spam/ham corpus at Habeas, and reached the same conclusion.


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