Cheers, found that thread in an earlier stage of its evolution, I believe.
So yay, we've got an interaction between one single mail client that happens to be the popular-default on its platform, and ... a slight indication that either of AT&T or Yahoo are possibly maybe aware of it should-have-been-fixed-a-week-ago?
The lack of technical detail is impressive (not that I expect a lot on Apple forums, and right now the last post seems to be an "I made toast and suddenly I got some mail so making toast must be important" red herring - or at least, I walked my user through the same to no avail, and POP was still fine for her while SMTP is the issue) ... kind of amazed they'd leave the entire? Apple userbase in the lurch for so long, but if I had to choose 2 or 3 corporate entities that would have to interact to resolve an issue...
Oh well, more searching for me. Apparently it's still a problem because no bolus of previously un-sendable mail has made its way to me yet.
[How's life for iPhone customers? Does iOS even use POP+SMTP in the default configuration?]