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Re: Fun new policy at AOL
From: Paul Vixie <vixie () vix com>
Date: 28 Aug 2003 18:10:51 +0000

Play with DNS MX records like QMTP does.

Something like

crocker.com.  MX      65000 trusted-mx.crocker.com.
              MX      66000 untrusted-mx.crocker.com.

there are at least two problems with this approach.  one is that an mx
priority is a 16 bit unsigned integer, not like your example.  another
is that spammers do not follow the MX protocol, they deliberately dump
on higher cost relays in order to make the victim's own inbounds carry
more of the total workload of delivery.  (additionally, many hosts do
more spam filtering on their lower cost MX's than on their higher cost
(backup?) MX's, and the spammers know this, and take advantage of it.)
Paul Vixie

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