said by NormanS:
Ma Bell was killed off in 1984, and she isn't coming back. What currently exists is more of a zombie, or a Frankenstein monster.
All email is now handled by Yahoo! severs, despite the aliases:
. . .
Yep, I was just being snarky. Mostly because it let me imagine the idea of "whups, lost access to a regional auth DB," which ... well, the history that results in the possibility of that sort of federation existing makes me wince and giggle in equal parts. 'Nothing personal!', just mind-boggling.
FWIW, if you notice, the various permutations of the various SMTP servers once/currently favored do resolve to slightly different permutations of CNAMEs with different addresses, so there was room to wonder if one might've dropped some such association while another did not.
Both POP3 and SMTP service had some issues with certificate expiration recently. I have no idea if that is the problem you are having.
That sounds promising - I'll have a look into it, although it made it to the point in the SMTP handshake to be rejected (or so the client seems to claim), so not so sure it'll be the culprit.
Anyhow, still an open issue until the wrench in the works is located or it magically goes back to working.