IMAP authentication problem

l2 l2 0 Βαθμοί φήμης
2026-08-24T01:03:48.1633333+00:00

I’m having an IMAP authentication issue with a personal Outlook/Hotmail account when using Thunderbird.

The account works normally in Outlook.com, and SMTP sending from Thunderbird also works correctly. However, IMAP access fails.

Settings being used:

IMAP server: outlook.office365.com

Port: 993

Security: SSL/TLS

Authentication: OAuth2

OAuth authentication completes successfully, but the IMAP server returns:

NO User is authenticated but not connected.

I have tested other Outlook/Hotmail accounts on the same computer and the same Thunderbird installation, and they work normally.

IMAP and POP access are enabled in Outlook.com settings, and the affected email address is the primary alias of the account.

Has anyone encountered this issue? Could this be an account-level IMAP provisioning/backend problem on Microsoft’s side?

Οutlook | Windows | Νέο Outlook για Windows | Για οικία
Οutlook | Windows | Νέο Outlook για Windows | Για οικία

Χρήση του νέου Outlook στα Windows για προσωπική διεύθυνση ηλεκτρονικού ταχυδρομείου, ημερολόγιο και διαχείριση επαφών

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  1. Ian-T 15,780 Βαθμοί φήμης Εξωτερικό προσωπικό της Microsoft Επόπτης
    2026-08-26T01:41:13.7966667+00:00

    Please note that this is Greek Q&A Forum, any threads should be posted in Greek. However, I will still provide an answer in English based on your initial response. 

    Hi @l2 l2

    Your IMAP settings are correct. Microsoft’s Outlook.com IMAP documentation confirms that outlook.office365.com, port 993, SSL/TLS, and OAuth2 are the supported settings.

    Because OAuth completes successfully, SMTP works, and other accounts work in the same Thunderbird installation, this does not appear to be a general Thunderbird configuration problem.

    Please feel free to try these steps:

    • Open Microsoft account Recent activity.
    • Find the sign-in event corresponding to the failed IMAP connection.
    • Expand it and select This was me.
    • Remove the affected account from Thunderbird, restart Thunderbird, and add it again using automatic configuration and OAuth2.

    IMAP connection errors can occur when an Outlook.com account is configured in multiple email clients and currently it's recommended authorizing the matching event through Recent activity.

    Hope this helps, please feel free to let me know if you need any further assistance

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