Is Hotmail in the habit of ignoring MX records?

Jimmy Hess mysidia at
Tue Jul 31 02:27:17 UTC 2012

On 7/30/12, valdis.kletnieks at <valdis.kletnieks at> wrote:
> On Mon, 30 Jul 2012 10:07:37 -1000, William Herrin said:
> The Internet uses DNS.  You use some other scheme at your own peril,

Aside from that RFC974 [Page 3] gives mailers significant leeway in
deciding how to handle errors:

"  Mailers are expected to do something reasonable in the face of an
error.  The behaviour for each type of error is not specified here,
but implementors should note that different types of errors should
probably be treated differently.  "

Attempting to find another path for an apparently unroutable message
(all MX offline) is not entirely out of the question.   You may not
assume that such measures will not be attempted,  if  anyone could
consider it a 'reasonable' error handling procedure.

I will echo that;  go back to the robustness principal of being
liberal in what you accept....  You should either  not listen on port
25,   or  you should  not  create that A record  pointing to a mail
server that won't actually accept mail.

When  ""   has an A record,   all the services
listening on that address are services for the domain.

"Relay not allowed"  to the same domain  may be considered
nonsensical,  and a mailer converting its error recovery attempt into
a permanent error at that point,  may be reasoned.


More information about the NANOG mailing list