Thunderbird cannot access Outlook email.

Question

I added an Outlook email account to the Thunderbird mail application.

However, the following message appears and the inbox remains empty:

“The current command did not complete successfully. Server response for account <PII removed>: User is authenticated but not connected.”

Could you please advise on possible solutions to this issue?

Below is the information about the environment and the troubleshooting steps already performed.

The account type is not personal but a “Work or School Account.”

The user is a standard (non-administrator) user.

The incoming and outgoing server settings, including authentication methods, have been verified and appear to be correct.

Disabling IPv6 had no effect.

Sending and receiving mail works normally when connecting via MAPI using the Outlook client.

The same issue occurs even when using a different device.

Changing the network environment does not resolve the issue.

The Microsoft Remote Connectivity Analyzer shows no problems in the connection test.

The issue occurs with accounts both with and without two-factor authentication enabled.

Regarding the configuration, there are two accounts (one standard user and one administrator) that were successfully added to Thunderbird and can send and receive emails normally. The settings were checked against those working accounts.

Thank you in advance for your assistance.

Answer 1

Hi @SAKAI A 

Thank you for posting your question in the Microsoft Q&A forum. 

Please note that our forum is a public platform, and we will modify your question to hide your personal information in the description. Kindly ensure that you hide any personal or organizational information the next time you post an error or other details to protect personal data.  

Thunderbird is a third‑party email client, so we don’t have deep expertise with its configuration details. Many users have reported similar issues, and one commonly suggested workaround is to disable IPv6. However, since that hasn’t resolved the issue in your case, it’s important to double‑check your account configuration against the guidance in this Thunderbird support thread. 

To make sure you get the most accurate guidance, I’d recommend also posting your question in the Thunderbird Help Community where experienced Thunderbird users and contributors can provide detailed troubleshooting steps. 

This information is provided as a convenience to you. These sites are not controlled by Microsoft, and Microsoft cannot make any representations regarding the quality, safety, or suitability of any software or information found there. Please ensure that you fully understand the risks before using any suggestions from the above link.  

Thank you for your understanding. 

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Answer 2

The error indicates that Thunderbird is authenticating the account but is not completing a modern (OAuth2) connection to the Outlook/Exchange Online service. For work or school (Microsoft 365) accounts, basic authentication is no longer supported, so Thunderbird must be configured to use OAuth2 for both incoming and outgoing connections, and in some cases the account must be removed and re‑added so that Thunderbird discovers the correct modern settings.

Try the following steps in order:

1. Confirm Thunderbird is using OAuth2 for IMAP/POP
   1. Open Thunderbird.
   2. Select ☰ (menu) > Account Settings.
   3. In the left pane, select Server Settings for the problematic Outlook/Exchange Online account.
   4. For Authentication method, change it to OAuth2 (do not use Normal password or other basic methods).
2. Confirm Thunderbird is using OAuth2 for SMTP
   1. In Account Settings, in the left pane select Outgoing Server (SMTP).
   2. In the right pane, select the Microsoft 365/Outlook SMTP entry for this account and choose Edit….
   3. Set Authentication method to OAuth2.
   4. Select OK to save.
3. Remove and re‑add the account so Thunderbird auto‑discovers modern auth Since the same account fails on multiple devices and networks, the profile configuration is a likely cause. Removing and re‑adding forces Thunderbird to detect the correct modern authentication and server settings.
   1. In Thunderbird, remove the problematic account from Account Settings.
   2. Restart Thunderbird.
   3. Add the work/school account again using Add Mail Account and sign in when the Microsoft sign‑in window appears.
   4. Do not override the discovered authentication method; let Thunderbird keep OAuth2.
4. Compare with working accounts There are two accounts that already work in Thunderbird. For the problematic account, ensure the following match one of the working accounts:
   • Server type (IMAP vs POP) and server hostnames.
   • Connection security (SSL/TLS settings).
   • Authentication method = OAuth2 for both IMAP/POP and SMTP.
5. If the problem persists
   • Verify with the Microsoft 365/Exchange Online administrator that IMAP/POP access is allowed for this specific work/school account and that any conditional access or security policies are not blocking IMAP/POP with OAuth2.
   • If IMAP/POP is disabled or restricted for that account, use Outlook (MAPI) or Outlook on the web instead, or request that the admin enable IMAP/POP with modern authentication for this mailbox.

These steps align Thunderbird with the required modern authentication (OAuth2) for Outlook/Exchange Online and typically resolve “User is authenticated but not connected” when other accounts on the same tenant work.

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References:

• Modern Authentication Methods now needed to continue syncing Outlook Email in non-Microsoft email apps
• Outlook and other apps are unable to connect to Outlook.com when using Basic authentication
• Set up email in Mozilla Thunderbird 8.0