try changing to outlook.office365.com and setting authentication to Oauth2

Thank you David. I finally figured out to what you were referring and as I could not respond to ask you for detailed step-by-step directions, I was able to Google search from my cell...One must go to Thunderbird, go to accounts and find "Server Name" - once you find that you can erase/delete the current name (I suggest writing it down in case the next step doesn't work you can always go back). Then you would enter "outlook365.com" or "outlook.office365.com" as the new server name and that solved my issue. All of my current and old emails were available...all 4,000+ new ones, ugh! As of 48 hours ago it is all working fine. I have not changed authentication. If I have more issues, then I will change that next.

By mid september, account wil fail if not Oauth2. That, per MS. I'm pleased all is working.

I have this problem too. Quite suddenly, every time I try to use Thunderbird on my Windows 10 64bit PC, up pops the message asking for the password for that email address. It is doing it every time, for each email address. The two email addresses are from different email providers. I put in the password, it tries to connect but this does not happen. Up pops a message, for retry, cancel, enter the password again. Why has Thunderbird suddenly lost my passwords, and why does it not remember when I put the password in the pop up box? I do not use any password managers. But even if I opt to save the password I enter to password manager, it does not connect to the servers.

I cannot find anywhere in Thunderbird account settings to input passwords to the email accounts. Account settings just has the words 'normal password', nowhere to put a new password in. I am using posteo and talktalk email providers.