Is Hotmail in the habit of ignoring MX records?

Ryan Rawdon ryan at
Thu Jul 26 14:05:55 UTC 2012

On Jul 26, 2012, at 2:14 AM, Lou Katz wrote:

> One of my users has reported incoming mail failures, which I finally
> tracked down. It turned out that Hotmail has seen fit to send the mail
> to his domain's A record machine, despite the fact that he has valid MX records.
> The A record points to my webserver, which does not normally accept mail
> for anyone. The mail server MX records are to an entirely different machine.
> Comments?
> Do I need more valium?

If you subscribe to and look in the archives, you'll see a thread named '[mailop] Hotmail ignoring MX, going direct to @ IN A?  ' from March of this year (which carries over into April).  In this thread Mark Foster encounters the same issue, and upon investigation others (including myself) see it as well.

I found that we were having the same issue after users on Hotmail were forwarding us DSNs regarding messages that our mail server had never seen, however upon checking our web servers for that hostname we found connections and delivery attempts from Hotmail.

Additionally, quoted from Tony Finch in the mailop thread regarding 'what if your MXes are broken and it is just failing back to A':

   If one or more MX RRs are found for a given name, SMTP systems MUST
   NOT utilize any address RRs associated with that name unless they are
   located using the MX RRs; the "implicit MX" rule above applies only
   if there are no MX records present.  If MX records are present, but
   none of them are usable, this situation MUST be reported as an error.

No solution to the issue was found in the various forks of that thread, however one individual afflicted by this issue (the OP) seems to have resolved his specific issue with Hotmail by fixing his MX records to be in stricter compliance with RFCs and best practices (removed a CNAME) - that said, per the quote above Hotmail should not have been falling back  to the A records or any other RRs for the hostname.

The matter is still unresolved for us and presumably others on the list except for the OP

> -=[L]=-
> -- 

More information about the NANOG mailing list