Bugzilla

I can confirm this issue is still present in Thunderbird 153.0 ESR on Linux Mint.

Environment:
- Thunderbird 153.0 ESR
- Linux Mint
- Microsoft Exchange Server 2019 (on-premises)
- EWS
- NTLM authentication

Observed behavior:

- Account setup succeeds.
- Folder hierarchy is downloaded.
- Sending mail works.
- Receiving mail works.
- Message bodies can be opened.

However Thunderbird continuously displays:

"Login to exchange.example.com with username username user.name failed."

The login dialog immediately reappears after pressing either Retry or Cancel, making Thunderbird unusable.

Despite the login dialog, the account continues to synchronize and send/receive mail successfully.

I verified that authentication itself is correct:

- curl --ntlm against the EWS endpoint authenticates successfully.
- Evolution EWS works with the same server, credentials and NTLM authentication.

As a workaround I had to manually remove the EWS account from Thunderbird's prefs.js because the endless login dialog prevented access to the Account Settings.
The username configured in the account was "Example User", but the login dialog repeatedly reported a failure for username "user.name".