What do you think is going to happen when you remove the account? or add it again for that matter. Unless the server names are wrong then you will be offered exactly the same authentication option after you do your thing and it will still not work. Most folk use oauth to access office365. You will certainly not be using the same URL to access mail in Thunderbird using mail protocols as you do when accessing it in a web browser. You do not even use the same servers. So please do not assume things. Some folk use an addon to access office265 where the admin has disallowed normal mail protocols that does use exchange server web services. Some of those URLS might be the same, I do not know anything about the addon really other than it exists. If you are accessing via an addon, then you should be seeking support via the addons support page not this product one. This support article from 2024 suggests that your use oauth authentication and enter your passkey when prompted in the authentication process. https://support.mozilla.org/en-US/kb/microsoft-oauth-authentication-and-thunderbird-202#w_your-outlook-or-hotmail-password-no-longer-works-with-thunderbird-and-you-cannot-send-or-receive-email