Ignoring MX records - how common

[Simon Waters]

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Mark_Andrews at isc.org wrote:
> 	
> 	It will be SPAM unless one of your nameservers is returning
> 	NODATA to MX requests.  You have to have a negative answer
> 	to the MX query before you make the A request.  Nameserver
> 	failure is *not* enough to cause fallback to A records.

Mark, you're assuming things all follow the RFC's, my question
is how many don't.

So far most stuff is spamware, but there are 2 distinct genuine
servers doing this (since one belongs to a DNS consultancy you
never know if their DNS is "fully debugged") to me.

I have found reports of Hotmail, and also IIS SMTPSVC doing this
 with form mail, but I can't confirm either as I don't regularly
get mail to the domain in question from either of these sources.
Beside if it claimed the sender was on hotmail I'd probably
assume it was spam without double checking.
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