I'm late to the party. Had the same issue.
tl;dr -- Microsoft removed the IPv6 AAAA record around 8:09pm US EDT (00:09
UTC) and all of our backed up email is now delivered successfully.
Long story:
We've been delivering to hotmail for years, and I've got logs going back to
May 29, 2022.
Microsoft added IPv6 AAAA records likely around Oct 24, 2022 at 21:06:13
UTC, as prior to that email, everything was IPv4 in the logs.
Everything was fine between 21:06:13 and 22:00:57, when, after 9 emails had
been successfully delivered, after almost 700,000 between May 29, 2022 and
Oct 24, 2022 were delivered without issue via IPv4, we received the dreaded
Deferred: 451 4.7.500 Server busy. Please try again later from
[2a01:111:e400:7e0d::51]. (AS750)
[HE1EUR04FT020.eop-eur04.prod.protection.outlook.com]
As Frank privately pointed out to me, some emails were delivered via IPv6,
389 to be exact, but many more were not, with a handful of emails still
being rejected from Oct 24 still today!
8 Oct 24
71 Oct 25
80 Oct 26
222 Oct 27
And after the IPv6 was removed, we delivered 1,178 emails in about 2-3
minutes.
So while the immediate outage is resolved, I'm not looking forward to the
next time this happens.
Cheers
Beckman, new subscriber because of this
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Peter Beckman Internet Guy
beck...@angryox.com https://www.angryox.com/
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