Installed new version of Thunderbird last night, now get error from MS on one account?

[SouthernGypsy]

After installing the newest version of Thunderbird last night I have started getting an error message on one of our Microsoft email accounts. The error message is;

The RETR command did not succeed. Error retrieving a message. Mail server outlook.office365.com responded: Server Unavailable. 21

This only just started after installing the newst update to Thunderbird last night, but only on my primary account. We each have personal accounts plus an account for our Ranch, six in total, and all of the others still work fine. All of our accounts use the same POP/Server settings;

Server Type: POP Mail Server

Server Name: outlook.office365.com

Port: 995

Connection security: SSL/TLS

Authentication method: OAuth2

And of course I double checked and POP is still Enabled on Microsoft/Outlook just as it always has been.

It says connecting, acts like it authenticated, but then pops up that error message, but if you watch the status line at the bottom it shows 37 new mails to download as though it's about to download them, but then doesn't.

Stange thing is that it's only my primary personal account that is having the issue, our other 5 accounts all still work as they should. It was working fine before yesterday evening when the Thunderbird update installed and I have not changed any settings. I did go in and double check all the settings anyway both in Thunderbird and on Outlook/Microsoft and everything is as it should be, yet suddenly I keep getting the error on the one account?

Anyone know what's going on with this newest Thunderbird update?

[Riodx]

Same issue here 
it seems that this is a Microsoft's issue something happened from their end and they won't say or even acknowledge what it is 
raised ticket and waiting to see what will happen 

[pcicu]

Same issue here.   This "The RETR command did not succeed. Error retrieving a message. Mail server outlook.office365.com responded: Server Unavailable. 21" problem has started several months ago. It comes (for 20 or 30 minutes) and goes away. I get it with POP at outlook.office365.com  .    I've been unable to get my organisation to take it up with Microsoft.   I wonder if Mozilla can do that, and/or if there's a way to update Thunderbird so that it does not happen any more! 

[MaRaNtZ]

I experience an even more strange problem using office365 outlook email and thunderbird (via OAUTH2).
It seem that the "release" channel do not authenticate anymore for reading IMAP email, but the ESR channel does work. I assume microsoft have changed something about "modern authentication" and newer thunderbird releases do not cope well with these internal changes... weird.

[wsm]

If you still see a problem with the newest versions, please post the details at https://support.mozilla.org/en-US/questions/new/thunderbird, state your version and whether you are using imap or pop accounts.