Pegasus worked perfectly - once I had persuaded Office 365 to offer me the App Password login option. I can't be sure exactly which part of the 365 druidic ritual was the magic setting.
Much head-banging and clicking various Office 365 admin offered links for Azure directory and 2FA to let user set their own password.
Still could not get an "App Password" option in the user's login options.
Finally in desperation: in my 365 admin it showed 2FA was "Enforced" for the user. Selected that drop down box's options and went for "change" and ticked the box for the user to re-enter their contact details.
Went back to the user login. Prompted to enter my details - and finally the method drop down box included "App Password".
Phone text 2FA had been set in the various stages above - so was then presented with the password (which I named Pegasus Mail) to copy to clipboard and save in NotePad. Changed my Pegasus IMAP password to the app one - and success! The same password was also used simultaneously in both my laptop and desktop.
I suspect I need to change my Pegasus POP3 and SMTP password entries as well - but I didn't push my luck. Apparently the old-style SMTP login still works as a provision for dumb printers that can't be upgraded.
A word of warning if you use Web access (OWA) for Office 365 email. Any aliases for incoming mails are still accepted - but you don't know which alias they used without digging into the raw headers. However - the Outlook design only allows outgoing emails to be FROM the default email address - no way to set an alias in the FROM. Fortunately Pegasus IMAP works perfectly with the 365 configured aliases for both send and receive.
Heartfelt thanks to David for v4.80
Pegasus worked perfectly - once I had persuaded Office 365 to offer me the App Password login option. I can't be sure exactly which part of the 365 druidic ritual was the magic setting.
Much head-banging and clicking various Office 365 admin offered links for Azure directory and 2FA to let user set their own password.
Still could not get an "App Password" option in the user's login options.
Finally in desperation: in my 365 admin it showed 2FA was "Enforced" for the user. Selected that drop down box's options and went for "change" and ticked the box for the user to re-enter their contact details.
Went back to the user login. Prompted to enter my details - and finally the method drop down box included "App Password".
Phone text 2FA had been set in the various stages above - so was then presented with the password (which I named Pegasus Mail) to copy to clipboard and save in NotePad. Changed my Pegasus IMAP password to the app one - and success! The same password was also used simultaneously in both my laptop and desktop.
I suspect I need to change my Pegasus POP3 and SMTP password entries as well - but I didn't push my luck. Apparently the old-style SMTP login still works as a provision for dumb printers that can't be upgraded.
A word of warning if you use Web access (OWA) for Office 365 email. Any aliases for incoming mails are still accepted - but you don't know which alias they used without digging into the raw headers. However - the Outlook design only allows outgoing emails to be FROM the default email address - no way to set an alias in the FROM. Fortunately Pegasus IMAP works perfectly with the 365 configured aliases for both send and receive.
Heartfelt thanks to David for v4.80