Forum Discussion
Outlook not syncing with 365. Connection Status Under Authn: Error
https://support.office.com/en-us/article/resolve-outlook-for-windows-issues-with-automated-troubleshooting-tools-38e2342d-3527-4190-8754-a82d8b970fe2
Yeah, it didn't really come back with anything. (Something about checking ignored conversations)
I've just had it happen to another user. Instead of nuking the profile, creds in cred manager, and the C:\Users\user\appdata\local\microsoft\outlook folder as I had been doing to those affected,
Saw someone post something about it being the fault of SDXHelper.exe. I closed outlook, killed the outlook.exe process as it was stuck, then killed two instances of SDXHelper.exe that were there. Launched outlook, and it instantly connected and all the messages left the outbox properly and continued syncing properly. Then, checked for office updates manually(it was already up to date). Don't know how long it will last.
So it appears a recent update somewhere made a change to SDXHelper.exe to reach a state that prevents Outlook from syncing properly. This has been observed on Windows 7 so far only, and with Outlook 2016 and Outlook 365 perpetual.
We'll also see if this is the case if and when the other machines exhibit the behavior again OR if other users start having it.
