[Fixed]: Thunderbird not Working with Office 365

Many users have reported encountering issues when trying to integrate Thunderbird with Office 365. There are several reasons for the Thunderbird not working with Office 365 issue. In this article, we will explore the reasons behind this issue and provide effective solutions to fix this issue.

Some common reasons that restrict Thunderbird from working with Office 365 are:

  • Incorrect Configuration Settings: Thunderbird may fail to connect to Office 365 if the configuration settings are incorrect, such as server addresses, ports, and encryption protocols.
  • Unsupported Protocols: Thunderbird uses IMAP (Internet Message Access Protocol) and SMTP (Simple Mail Transfer Protocol) to communicate with email servers. If your Office 365 account does not have IMAP or SMTP access enabled, Thunderbird will not be able to connect.
  • Authentication Issues: Office 365 requires specific authentication methods, such as OAuth 2.0 or app passwords. If Thunderbird is not using the correct authentication method, it may fail to connect with Office 365.
  • Firewall or Antivirus Interference: Sometimes, security software or firewall on your computer can interfere with Thunderbird's communication with Office 365. These applications may block certain ports or protocols used by Thunderbird, causing connectivity issues.
  • Outdated Thunderbird Version: If you are using an outdated version of Thunderbird, it may not be compatible with Office 365.
  • Server Issues: Sometimes, temporary server issues on the Office 365 side can affect Thunderbird's connection.

Solutions to Resolve Thunderbird not working with Office 365

You may encounter various error messages and issues when Thunderbird not work or connect with Office 365. Below, we will be discussing different issues and their respective solutions.

Issue 1: Thunderbird IMAP responded: User is authenticated but not connected.

Thunderbird client cannot connect to the outlook.office365.com IMAP server even after deleting the stored token. Even after following the connection procedure to connect again, it does not work. The user receives two error messages:

  • The current operation on 'inbox' did not succeed. The mail server for account ... (IMAP) responded: User is authenticated but not connected.
  • Server outlook.office365.com has disconnected. The server may have gone down or there may be a network problem.

Solution: If you are using the old version of Thunderbird, then try updating it to the latest version (Thunderbird 102.6.1). If your Thunderbird is updated, then check IPv6 settings by following these steps:

  • Click on the gear icon (at the bottom left).
  • Click on General to check the settings.
  • On the extreme right of the bottom corner, you will find Configuration Editor. Click to see all.
Configuration Editor
  • Type network.dns.dis in the search field.
  • Select the first option network.dns.disableIPv6 and then click on the toggle arrow on the right to change it into ‘True’.
  • Now close the window and reopen Thunderbird.

Issue 2: Thunderbird failed to work with Office 365 emails.

A lot of Thunderbird users encountered this issue while using Office 365 on Thunderbird (POP). They continuously receive message, “Log in failure: unknown username or incorrect password”.

Solution: When adding your Outlook.com account to Thunderbird, you might require the POP, IMAP, or SMTP settings for Outlook.com. Here are the manual server settings that are required.

  • IMAP server name outlook.office365.com
  • IMAP port 993
  • IMAP encryption method TLS
  • POP server name outlook.office365.com
  • POP port 995
  • POP encryption method TLS
  • SMTP server name smtp-mail.outlook.com
  • SMTP port 587
  • SMTP encryption method STARTTLS


  • Incoming and outgoing server details are the same.
  • POP access is disabled by default.
  • Outlook.com does not require Secure Password Authentication (SPA).

Since POP access is disabled by default, you are required to enable POP access. Follow the steps given below to enable POP access:

  • Select Settings > View all Outlook settings > Mail > Sync email.
  • Under POP and IMAP, select Yes under Let devices and apps use POP.
  • Select Save.

Note: If the solutions provided above do not work, you can re-install the Thunderbird application. But, before uninstalling the app, take the back up of your profile folder.

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To Conclude

Thunderbird is not officially supported by Office 365. However, many users successfully use Thunderbird with Office 365. Occasionally, some issues arise due to which they’re not able to connect the Thunderbird with Office 365. If you’re one such user and continue to experience issues, you may consider using an email client officially supported by Microsoft, such as Outlook. You can switch to Outlook and migrate or transfer all your Thunderbird mail data to Outlook. However, the manual process to migrate data from Thunderbird to Outlook is not easy as both email clients use different file formats to store the data. This is where an MBOX to PST converter tool, such as Stellar Converter for MBOX comes into picture. It easily and quickly converts Thunderbird MBOX file into PST that you can easily import into Outlook.

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About The Author
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Shelly Bhardwaj linkdin Icon

Shelly is technology expert and core knowledge of Exchange Server, Outlook.

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