Thunderbird コミュニティフォーラム

I can't add my personal @hotmail.com account to Thunderbird. Every attempt ends with "Authentication error – Unable to log in at server. Probably wrong configuration, username or password." All my other accounts (Gmail and several Microsoft 365 business accounts using outlook.office365.com + OAuth2) work fine in the same profile.

Setup

• Thunderbird 160.0 (64-bit) on Windows (problem also happened on 159.0)
• Settings auto-detected by the Account Hub: IMAP outlook.office365.com:993 SSL/TLS OAuth2; SMTP smtp-mail.outlook.com:587 STARTTLS OAuth2
• POP3 (outlook.office365.com:995 SSL/TLS OAuth2) fails in exactly the same way

What happens

• The Microsoft sign-in opens in my default browser, I sign in with the correct account (2FA), and I get the "You're all set" page.
• With mailnews.oauth.loglevel = All, the Error Console shows a successful token response from login.microsoftonline.com with scopes IMAP.AccessAsUser.All, POP.AccessAsUser.All and SMTP.Send, and "Creating new login for ...@hotmail.com". Microsoft also emails me "New app(s) connected to your account".
• Immediately after that, account setup fails with "Unable to log in at server". The console shows nothing more specific.

What I already tried

• Removed and re-added the account several times; cleared the saved OAuth logins for this address
• Cookies are allowed; mailnews.oauth.useExternalBrowser is back to true (setting it to false made the redirect go to https://127.0.0.1 and fail)
• In Outlook.com: IMAP is enabled (toggled off/on and saved). The address is the primary alias of the Microsoft account. Two-step verification is on. Recent activity shows no blocked or unusual sign-ins, even right after a failed attempt.
• Webmail works normally.
• Microsoft support says nothing is blocked on their side and sent me here.

Is there anything else I can check, or a way to see the actual IMAP server response to find out why it rejects the token?

When using the retention policy "delete all but the most recent x messages" on an IMAP folder on Thunderbird 160, I am seeing messages get deleted from Thunderbird but they are still present in webmail.

When using the retention policy "delete messages more than x days old", the messages get deleted from both Thunderbird and webmail as I would expect.

I have restarted Thunderbird and run a repair on the folder, but nothing changed.