Re: IP filtering based on corresponding MX records
- From: "Rich Matheisen [MVP]" <richnews@xxxxxxxxxxxxxxxxxxxxx>
- Date: Tue, 17 Oct 2006 14:59:29 -0400
"james chong" <jamestechman@xxxxxxxxx> wrote:
I believe you're talking about Exchange trying to perform a forward
lookup during the HELO initiation. I don't think Exchange can do this.
I'm not sure if you're trying to incoporate this as part of your SPAM
solution or trying to explicity block a domain or not, but most people
will tell you that blocking soely on foward on reverse lookups is not a
comprehensive solution. In addition blocking solely on failed forward
lookups does not comply with RFC protocol.
Spam is war. Sometimes you just gotta ignore the RFC's, although I'm
not sure which one you found that in.
If someone's using a phoney domain name to send mail, who cares if you
drop the message? You'd never be able to reply to it, you'll never be
able to send a NDR to it.
I'd agree that reverse lookups are of dubious value. But a failed
forward lookup? Oh, yeah . . . it's junk. Don't send a 250, send a 5xx
or a 4xx (if you think that its just a transient DNS problem) as the
status for the MAIL FROM. Either that or give it a pretty high ranking
in your evaluation of the message's spamminess.
--
Rich Matheisen
MCSE+I, Exchange MVP
MS Exchange FAQ at http://www.swinc.com/resource/exch_faq.htm
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