Is Hotmail in the habit of ignoring MX records?

[mysidia at gmail.com (Jimmy Hess)]

On 7/26/12, Lou Katz <lou at metron.com> 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.

You looked in the mail headers and saw hotmail's mail server do that,
or the From address/return path just happens to be hotmail?
I would ask for a specific example of a domain name in which that
seems to happen, and  exact DNS zone contents.

I am sure that Hotmail does not  ignore MX in general,  unless they
just broke something; many domains require MX processing and A record
to properly be ignored for mail to be accepted.    But there may be
something else going on with a specific domain or   DNS
queries/responses from its nameservers,  that results in MX being
ignored or unavailable,  resulting in a fallback to 'lookup A'.

An example could be some dns issue such  as slow response to MX query,
 'MX to a CNAME',  'MX to an invalid label that looks like an IP',  MX
DNS response packet too large,
 ....


--
-JH