At&t (yahoo) email (send) stopped working yesterday

Have long used, stable emclient installation (ver 7.2.34959.0) that now fails when attempting to send email. Receive is fine. No changes have been made, ANYWHERE on my system. Errmsg when attempt to send email:
“[SMTP] An attempt to connect to tvvaught@att.net failed. This could be caused by temporary server unavailability or incorrect settings. Do you want to check the settings?”
I’ve been going around in circles on the at&t support site, with no help so far. I really hate to start changing settings, willy nilly, without a reason, as that technique usually just confuses matters more. Any ideas?

Check https://www.emclient.com/release-history?os=win

Thank you sunriseal for ref to emclient updates available a/o today. Unfortunately, the error persists. I installed the 7.5.2 update, then the 8.0 update, with no change in symptoms. I’m going to reboot all, then dig some more…

OK, I’m good!
In addition to updating eMClient to version 8.03, I then regenerated (on at&t website) the “secure mail key” to a new number, then applied it to BOTH send and receive functions in the eMClient account setup area. In my case, I updated pop and SMTP authentication with the new key, tick the boxes “server requires authentication” and “use these credentials”.