Just to add one thing - with davmail, syncing is significantly slower but at least it works.
I took the easy/safe way out - have mbsync talk to davmail instead as that seems to work.
I did see #22 but that error is "unexpected tag" and this is why I opened this ticket instead. We moved to O365 about 3 months ago. mbsync runs every 10 minutes but at no point during this time did it complete. Any suggestions for anything to try?
Fails with "bad command" on some mails when syncing O365
Couple of things: The repo's last commit was in 2018 but 3.1.0.1 was released in 2020. Has the repo moved? Version 3.1.0.1 registers itself as version 3.1.0 in the registry's uninstall section.