@ThomM
No, the mail sent 2nd February at 16:21 was NOT sent by new-Mac, but by a Synology NAS (using identical mail settings, but they display differently in the Synology of course).
I checked: there were ZERO mails send attempts by either of the two new-Macs
…after the software updates late evening 1st February and
…before my mail +/- 18:00 that retuned the smtpauths “Offline” error.
I tried the four bluewin mail accounts on my new-Mac, and the three bluewin mail accounts on my wife’s new-Mac: receive worked; send failed.
This morning, my old-Mac and my wife’s old-Mac function correctly for all bluewin accounts.
1st February Apple update seems to be the culprit for the new-Macs.
Strangely, I have the same issue with two iPhones: both show an update pending but not yet applied. Unfortunately I have no idea how to access iPhone logs.
…investigation continues.
Chris