Hotmail/Outlook/Microsoft Email Switches to IPv6, Causing Email Failures

At Oct 24 21:06:13 UTC, after years of being IPv4-only, Microsoft Hotmail
published two IPv6 records for the MX record.

Great! Progress! Hurrah!

Except that one hour later, Oct 24 22:00:57 UTC, our IPv6 address was
blocked, after just 9 emails sent, as "spam."

Prior to this date, as far back as our logs go, we have had ZERO issue with
the almost 700,000 emails sent and accepted by Hotmail users since May 29,

So I visited the trusty Smart Network Data Service and Junk Mail Reporting
Program to try to troubleshoot. Except that these two services are still
IPv4-only, so I cannot even attempt to try to self-troubleshoot why
Microsoft is blocking email via IPv6.

I have opened a support ticket, but I figured I would see if anyone here
has seend or heard or had this issue, or if any Microsoft lurkers might see
this and investigate. Support request number: SR1543766049

I have not been able to find any mention in Google or elsewhere of the
planned switch to enable IPv6 for Hotmail, nor any updated way to register
with Microsoft with IPv6 address space.

Yes, we sign with DKIM and have up-to-date SPF records with both IPv4 and
IPv6 addresses. Google seems to have no issue here.

Thanks All


SERVICE SEEMS RECOVERED as of 8:09pm EDT Oct 27, 2022

It looks like lots of complaints finally got a change made -- the hotmail MX
records have removed IPv6 AAAA records from DNS, and now all of our 945 delayed
emails are delivered.

The AAAA records were removed sometime between 6:49:28pm EDT and 8:13:52pm
EDT. Logs show that sendmail stopped trying IPv6 at 8:09:11pm EDT and went
back to IPv4, and then all emails were accepted finally. Seems like that was
about the time that either the DNS record expired or when Sendmail got around
to checking DNS again.

30 second TTL on the record for so
it does seem like the change happened very recently.

Thanks to whomever finally took action to resolve it! And to Microsoft,
please update all of your Email Service Provider functionality to support
IPv6 BEFORE enabling it again please!