[Fixed]: Thunderbird not Working with Office 365

If you cannot use Thunderbird with Office 365 (Microsoft 365), it is mostly due to wrong server or authentication settings. There are, however, many other reasons that can result in this problem. In this guide, you’ll get to know the reasons why Thunderbird cannot connect to outlook.office365.com and the solutions to fix the issue.

Why is Thunderbird not Working with Office 365?

According to the Microsoft document, the company has removed the Basic Authentication method for Exchange Online (Microsoft 365). It introduced 'OAuth 2.0' or Modern Authentication – a more secure way of accessing the applications. This shift affected many Office 365 users who had configured their profiles in Thunderbird. There are some other reasons as well (mentioned below) because of which users are facing the Thunderbird not working with Office 365 issue.

• Firewall or antivirus blocking the required port (Port 587) to connect with O365
• Outdated or legacy version of Thunderbird lacking support for OAuth 2.0
• Incorrect IMAP/SMTP configuration settings (server addresses, ports, and encryption protocols, etc.)
• Temporary server or network problems
• Azure AD Conditional Access Policies blocking ‘legacy’ apps from connecting with outlook.office365.com.

What are the Ways to Fix Thunderbird not working with Office 365 Issue?

Below, we have mentioned some troubleshooting methods or solutions to fix this issue.

Method 1: Update the Mozilla Thunderbird

Mozilla's official release notes state that the legacy versions – v102.7 and earlier – did not support Microsoft Modern Authentication or OAuth2 protocols. So, there was no way to configure O365 accounts at that time. Hence, if you are unable to configure a Microsoft 365 account in Thunderbird, install the updates.

Here's how to do it:

• Launch Thunderbird application on your PC.
• Click on the Settings icon at the bottom left corner.
• Scroll down to the Updates section.
• Click on Update to <version>

Now, retry connecting to Office 365.

Method 2: Remove Old Saved Passwords

The Thunderbird application, at times, stores the old Basic Authentication credentials that may cause the “login to server outlook.office365.com with username failed Thunderbird” error. To resolve this, you can remove all the old passwords and try to reconnect to the account. Follow these steps:

• Open Thunderbird.
• Go to Settings > Privacy & Security.
• Scroll to Passwords.
• Click on Saved Passwords.

• The Saved Logins window will appear. Select the following accounts:
  • outlook.office365.com
  • smtp.office365.com
• Click Remove to remove all passwords.

• Restart Thunderbird.

Try to connect your account again using OAuth2.

Method 3: Enable Modern Authentication (OAuth2) in Thunderbird

Some users turned ON Modern Authentication in Thunderbird settings and fixed the 'Thunderbird not working with Office 365' issue. You can try this too and see if it works for you. Here are the steps:

• Launch Thunderbird.
• Click on gear icon at the bottom left corner.

• Click on Account Settings.

• Select the Office 365 account from the left panel and click on Server Settings.

• Choose OAuth2 Authentication method from the dropdown list.
• Restart Thunderbird and see if the issue is resolved or not.

Method 4: Check the IPv6 Settings

Thunderbird client cannot connect to the outlook.office365.com IMAP server after deleting the stored token. Even after following the connection procedure to connect again, it does not work and displays these 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.”

To check IPv6 settings:

• 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 the Configuration Editor. Click to see all.
• 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 to True.
• Close the window and relaunch Thunderbird to check if the issue is resolved.

Method 5: Reconfigure POP/IMAP/SMTP Settings Manually

When adding an Office 365 account in Thunderbird, incorrect SMTP/IMAP/POP settings may generate the following error message – “Log in failure: unknown username or incorrect password.” To fix this, you can check and reconfigure your email account in Thunderbird and add correct network settings. Here is how to do so:

• Launch Thunderbird on your Windows PC.
• Click on Email under the Set Up Another Account section.
• Add your email account credentials and click Continue.

• Click on Configure manually and enter the following IMAP/POP3 settings:

For Incoming Server

In case of IMAP:

• Protocol: IMAP
• Hostname: outlook.office365.com
• Port: 993
• Connection security: SSL/TLS
• Authentication method: OAuth2
• Username: your email ID

In case of POP3:

• Protocol: POP3
• Hostname: outlook.office365.com
• Port: 995
• Connection security: SSL/TLS
• Authentication method: OAuth2
• Username: your email ID

Outgoing Server

• Hostname: smtp.office365.com
• Port: 587
• Connection security: STARTTLS
• Authentication method: OAuth2
• Username: your email ID

• Click Done and follow the onscreen instructions to complete the process.

Thunderbird Still not Working with Office 365? Switch to Outlook

No resolution even after trying the above workarounds? Consider giving another email client – Outlook for Windows – a try. It works perfectly with Office 365. Here's why you should switch:

Here's why you should switch to Outlook:

• Your organization uses Exchange/M365 as primary mail server
• There is a need for collaborative tools, like Teams, OneDrive, etc.
• If you want calendar and contact integration in the system

For this, you'll have to first export all the Thunderbird mailbox data to an MBOX file and then convert it to PST format using Stellar Converter for MBOX - a professional MBOX to PST converter tool.

Recommended by IT professionals and admins, this advanced MBOX to PST converter tool lets you scan and convert MBOX, MBX, and RGE files of various prominent email clients, including Thunderbird, Apple Mail, Gmail (Google Takeout), PocoMail, Eudora, and more.

Here are some highlights of this tool:

• Accurately converts MBOX file of any size to PST file format
  Retains original mailbox structure and folder hierarchy after MBOX file conversion
• Saves mailbox items in commonly used file formats - EML, MSG, HTML, RTF, and PDF
• Converts and saves individual mailbox folders/items

Supported MBOX-based email clients include: Apple Mail, Eudora, and Entourage

Related Read: How to Migrate Thunderbird to an Office 365 Account?

Conclusion

If your Thunderbird app is not working with Office 365, switching to Outlook and migrating or transferring all your Thunderbird mail data to Outlook is your best option. However, it isn't easy as both email clients use different file formats to store the data. This is where Stellar Converter for MBOX - a specialized MBOX to PST converter tool, comes into picture. It easily and quickly converts Thunderbird MBOX file into PST that you can import into Outlook. This DIY tool also allows you to directly export MBOX data to Office 365. Additionally, you can use it to save items from an MBOX file PDF, RTF, HTML, etc.