Exchange Connection Problems

Fix Thunderbird IMAP OAuth Authentication Problems with Microsoft 365

Maira Mehtab Oct 22, 2026 869 views

Question details

Users experience repeated authentication requests or setup failures when configuring Thunderbird with Microsoft 365 IMAP via OAuth.

Fix Thunderbird IMAP OAuth Authentication Problems with Microsoft 365

Product: Mozilla Thunderbird / Microsoft 365
Device & OS: not provided
Scenario: Setting up or syncing a Microsoft 365 email account in Thunderbird using IMAP and OAuth2 authentication.
Observed behavior: Thunderbird repeatedly prompts for the Microsoft 365 password, fails to retain the OAuth token, or cannot complete the initial account setup despite IMAP and MFA being active.

Before you start

Ensure you have your Microsoft 365 login credentials ready and verify with your administrator that IMAP access is enabled for your specific mailbox in the Exchange Admin Center.

Solution 1Recommended

Update Thunderbird to the Latest Version

Updating resolves known bugs with OAuth2 authentication that affected specific Thunderbird releases (such as 102.7.0).

Certain builds of Thunderbird introduced a bug affecting Microsoft 365 OAuth2 token retention. Updating the application is the primary step to ensure these known issues are patched.

Open Thunderbird settings

Launch Mozilla Thunderbird and click the menu button (three horizontal lines) in the top-right corner of the window.

Check for updates

Navigate to Help and select About Thunderbird. The application will open a new prompt and automatically check for available updates.

Install and restart

Allow the update to download and install. Click the Restart to Update Thunderbird button, then test your Microsoft 365 connection again to see if the OAuth prompt functions normally.

Update Thunderbird to the Latest Version

Ongoing Bug Reports: If the problem persists in newer versions (e.g., 102.8.0), the bug may still be unresolved for your specific environment. Proceed to re-create the account or monitor Mozilla support channels.

Solution 2

Remove and Re-create the Microsoft 365 Account

Re-adding the account forces Thunderbird to generate a fresh OAuth token and correctly register the authentication protocol.

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Frequently Asked Questions

Why does Thunderbird keep asking for my Microsoft 365 password even when it's correct?

This usually occurs when Thunderbird's OAuth2 token expires or is rejected by Microsoft's servers due to a known bug in specific Thunderbird versions (like 102.7.0). It can also happen if your incoming server authentication method is mistakenly set to 'Normal Password' instead of 'OAuth2'.

How do I ensure IMAP is enabled for my Microsoft 365 account?

You or your organization's IT administrator must log into the Microsoft 365 Exchange Admin Center. Go to Mailboxes, select your user account, click 'Manage email apps settings', and verify that the IMAP toggle is switched to the 'Enabled' position.

What should I do if the latest Thunderbird update doesn't fix the OAuth token issue?

If you are using a newer version (like 102.8.0) and still face the issue, try clearing saved passwords manually. Go to Settings > Privacy & Security > Saved Passwords, delete the Microsoft 365 entries, restart Thunderbird, and let it prompt you for a fresh OAuth login.

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