IPv6 addresses for Microsoft Office 365 hosted domains?

[Frank Bulk]

This afternoon I saw several log messages in our email server's logs in
relation to emails our local business customer (who uses our ISP email
server) was trying to send to a Microsoft Office 365 hosted domain:

"[::ffff:12.43.166.xx] Site <target domain redacted>
(2a01:111:f400:7c0c::11) said after data sent: 554 5.7.1 Service
unavailable, message sent over IPv6 [2607:fe28:0:4000::10] must pass SPF or
DKIM validation (message not signed)"

The PTR for 2a01:111:f400:7c0c::11 is
mail-by26c0c.inbound.protection.outlook.com.  

But when I check the MX record of the target domain I see there's no AAAA
for the <redacted>.mail.eo.outlook.com, just three A's.

Fortunately we control our local business customer's DNS and I've added in
our email server's DKIM so that future emails, if they were sent over IPv6,
should be accepted by Microsoft.  Our customer has no SPF record.


I also saw two log messages for two Microsoft Office 365 hosted domains:
26 13:30:59.00 [56882563] Failed ::ffff:199.120.69.25
<notification+kyg2kgex at facebookmail.com> <target domain1 email redacted>
9259 <1502549920004098-1497189607206796 at groups.facebook.com>
"[::ffff:199.120.69.25] ubad=0, Site (target domain1
redacted/2a01:111:f400:7c10::1:10) said: 550 5.2.1 Service Unavailable,
[target domain1 redacted] does not accept email over IPv6"
26 19:04:52.00 [83985160] Failed ::ffff:12.43.166.20 <from redacted> <target
domain2 email redacted> 6546 <0EBCBB96763E41B2A4CD9A4CD3DD94BE at sp.local>
"[::ffff:12.43.166.20] ubad=1, Site (target domain2 email
redacted/2a01:111:f400:7c0c::11) said: 550 5.2.1 Service Unavailable,
[target domain2 email redacted] does not accept email over IPv6"

There's no PTR for 2a01:111:f400:7c10::1:10.  I checked the last 7 days of
logs I only saw these today.  

It's like Microsoft published some AAAA's for some MX records, but then
withdrew them, but not before there were a few failures.
 
Frank