https://support.mozilla.org/kb/microsoft-oauth-authentication-and-thunderbird-202

Yep, went through all that a few times. No go. The account works, just sometimes takes up to twenty tries to get it done. When I changed the Authorization method to OAuth2, it kept asking for my hotmail credentials - I would enter them and click next and the Request for Credentials would just pop up again, and again, and again. The other three accounts work fine and no issues. Frustrating as whenever I check, I have to delete twenty or thirty failure notices. It will download messages sooner or later and I have no problem logging on directly through Outlook.com.

When I changed the Authorization method to OAuth2, it kept asking for my hotmail credentials - I would enter them and click next and the Request for Credentials would just pop up again

Did you allow cookies in Thunderbird?

Yes, it is set to "Accept cookies from sites"

It seems to be cyclic. It can go for a day or so with no problem then for days with continuous failed attempts. I would blame the computer (Desk top Windows 10) but I have done nothing to change things, run both Virus (zone Alarm) and malware (Malware Bytes) scans.

You can try to start Windows 10 in safe mode with networking enabled.

Does the problem go away?

Windows safe mode disables anti-virus software. This is a troubleshooting step, not a solution.

I will run in safe mode for a couple of days and let you know here. Thanks.

Finally looks like I am able to respond again here on the forum. I ran W-10 in safe mode for a couple for a few days and same results. For a half hour at a time all I get is

Sending of password for user XXX@hotmail.com did not succeed. Mail server pop-mail.outlook.com responded: Authentication failure: unknown user name or bad password.

If I go away and come back in an hour or two, my emails have downloaded so the issue is intermittent and sometimes goes away for the day. I have tried changing the Authentification method from Normal Password to OAuth2 but then every time it tries to check for mail I have to put the password in again. Might as well just leave the Hotmail account running. It is frustrating because I have had this address working on TB since 2006 and it started doing this about 3 weeks ago and 3 other Hotmail addresses on my TB account work fine. Any ideas?

Try using the correct settings for hotmail/outlook/live accounts:

https://support.mozilla.org/en-US/questions/1417298#answer-1588949

For POP, the settings are the same except the port is 995.

Thanks sfhowes. I am using the correct settings. The same settings I have been using for many years and exactly the same settings as my other three accounts which work fine. The only thing that I have not tried is deleting the account and re-installing it but I am afraid if I do that I will lose all of my history for that account.

The error in your previous reply refers to pop-mail.outlook.com, not outlook.office365.com.

You won't lose your existing POP mail if you re-add the account, but the new account will use a different folder, e.g. outlook-1.office365.com.

Confirm you have all the correct settings, remove the entries from Saved Passwords in Settings/Privacy & Security, restart TB, enter the account password in the OAuth window. Since you have multiple accounts, check that each one is sending on an smtp with matching User Name (email address), i.e. one smtp for every account, even if they're on the same server.

Thanks sfhowes - Yep, all that done - I do not ever save passwords and I have tried both pop-mail.outlook.com, and outlook.office365.com. I would say that it looks like a W-10 problem but the other three with identical criteria work fine. I would also suspect Hotmail/Outlook except, again, three others with identical criteria work fine. I read somewhere that some accounts based out of the Dublin Microsoft servers were having problems and for a time a couple of months ago this address was taking hours for incoming emails to transit so I wonder if there is some way I can check where the addresses are domiciled? Right now my options are just wait and eventually the emails come through or have the emails from that account forwarded to a gmail account and then to my TB account which seems to work as well. From what I see, I am not missing any emails, just getting the error message 5 to 10 times in a row then the emails come in.

In case anyone is interested, I started this help request on Feb 10, 2024 and it is now March 27, 2024. I hav tried all suggestions and everything I could find on the internet and still the problem occurs. I have found a partial solution by having the problematic hotmail address forward all emails to one of the other three hotmail addresses that work fine. Not a good solution as there is a lot of wastage and duplications now but it does work. I have discovered two things that may matter. 1) the cantankerous hotmail address is domiciled in the Dublin servers and the other three are domiciled elsewhere and 2) the problem does not seem to happen with non-hotmail addresses - I have a gmail address - but that does not mean much since 3 of my 4 hotmail addresses work fine as well. At this point I doubt very much that I will find an answer to this issue so I will just have to wait it out or look for an email controller that is a little more friendly with Hotmail. Thanks everyone for your suggestions.