Easy Way to Fix the ‘Thunderbird Not Working with Office 365′?

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  • Updated on
    October 6th, 2025
  • Read Time
    6 minutes
Introduction: Mozilla Thunderbird is the best desktop-based email service. This email client is a free open-source email client. Sometimes, the configuration could not be verified to Office 365 due to various issues. As a result, Thunderbird not working with Office 365 issue arises and users seek a reliable solution to resolve it. To ease your workload, we have researched the issue and found an appropriate solution. Most people choose Thunderbird Backup Tool for a hassle-free outcome. Let’s go sequentially and understand the reasons first.

Like you, many users encounter the same situation when Mozilla Thunderbird works with Office 365. However, Thunderbird failed to connect to Office 365 due to various reasons. Let’s explore the different reasons for the situation. So, you can avoid and fix it. 

Reasons: Thunderbird is Not Working with Office 365

Here, read this section carefully to understand the different perspectives on the issue. So, you can avoid it from occurring in the future as well. 

  • This could happen when you configure Thunderbird to Office 365 incorrectly. 
  • If IMAP or SMTP is disabled in Office 365 account, Thunderbird cannot work with Office 365. 
  • When you use the wrong Thunderbird authentication, the configuration with Office 365 will be a failure. 
  • There are chances of server issues that constrain Thunderbird from working with Office 365. 
  • Check whether you are using the latest version of Thunderbird instead of the outdated version. 

Thus, these issues restrict you from connecting your Thunderbird email client to Office 365. Moving forward, we will discuss the problem along with its solution. 

Solutions: Thunderbird Failed to Connect to Office 365

In this section, we have covered different problems. Also, the solution for the issue, the configuration could not be verified to Office 365. 

Scenario 1. When User Authenticate But not Connected: IMAP Response in Thunderbird

The situation where authentication is done but users are still disconnected. In that scenario, IMAP responds with the two messages. 

  • When the recent operation on the inbox is unsuccessful. The IMAP response as User is authenticated but not connected. 
  • The outlook.office365.com server is disconnected. It could be because of server downtime or network issues. 

Before we begin the solution, check whether your Thunderbird is in the updated or latest version. If your Thunderbird is up-to-date, visit the IPv6 settings and follow the below guidance. 

  1. Launch Mozilla Thunderbird Account. 
  2. Tap on the gear icon at the extreme top-left corner. 
  3. Now, tap on the General option from the left-top corner. 
  4. Select the Configuration Editor at the end. 
  5. Type the network.dns.dis in the dialogue box. 
  6. Choose the network.dns.disableIPv6 and press the toggle to change from false to true. 
  7. Next, close the Thunderbird application and restart it. 

Scenario 2. Failure: Thunderbird not Working with Office 365

Sometimes, when configuring Thunderbird to Office 365, you might have received the message – Log in failure: unknown username or incorrect password. So, when you add Thunderbird to Office 365, check for these details and change it accordingly. 

In IMAP

  1. Server name- outlook.office365.com.
  2. Port- 993.
  3. Encryption method- TLS.

In POP

  1. Server name- outlook.office365.com.
  2. Port- 995.
  3. Encryption method- TLS. 

In SMTP

  1. Server name- smtp-mail.outlook.com.
  2. Port- 587.
  3. Encryption method- STARTTLS. 

Well, the POP is a disabled default, you have to enable it. Now, follow the given steps to enable POP. 

  1. Tap on the Settings option >> View all Outlook settings option. 
  2. Now, click on the Mail tab >> Sync Email option.
  3. In the Let devices and apps use POP, choose Yes. 
  4. Lastly, press the Save button. 

Still, you cannot connect to Thunderbird to Office 365. You can read the below procedure. 

Automated Software: Thunderbird Not Working with Office 365

The MacSonik Thunderbird Backup Tool is the ultimate option when the above solution cannot resolve your problem. Unlike other solutions, it will transfer the Thunderbird data into the Office 365 email client. Also, the process will be efficient and effective. If your Thunderbird failed to connect to Office 365, transfer the data into multiple file formats including MBOX, PST, etc. Also, you can Backup Thunderbird Emails to External Hard Drive. 

Steps to Resolve Thunderbird is not Working with Office 365

When Thunderbird failed work with Office 365 emails, follow the guide to resolve the issue. 

  1. Download the MacSonik Thunderbird Backup Tool on your PC. 
  2. Enter the profile from which you want to migrate the data. 
  3. Pick the Thunderbird Folder from the tree structure mailbox. Press Next. 
  4. Next, select the Office 365 email client from the saving options menu. 
  5. Sign In to the Office 365 account and use software features if required. 
  6. Press on the Convert tab to migrate the Thunderbird data into Office 365. 

Thus, these steps will assist you in migrating the Thunderbird data into Office 365 directly. So, you can access the Thunderbird data in Office 365 easily. 

Summarizing

when you go through this blog, you will get the solution to fix the issue- “Thunderbird not working with Office 365”. However, we provide two suitable methods: manual and Professional. In case, the manual solution didn’t work, try the Thunderbird Backup Tool to resolve your query. It will help you to complete the process without issues or complications.

Frequently Asked Questions

Q1. Why is Thunderbird not connecting to Office 365?

Ans: Thunderbird may fail to connect to Office 365 because of incorrect IMAP/SMTP settings, outdated Thunderbird versions, or disabled protocols. You can fix this issue by verifying server details and updating Thunderbird. However, if the manual process seems complex, using the MacSonik Thunderbird Backup Tool is a quick and reliable way to transfer or reconnect Thunderbird emails with Office 365 seamlessly.

Q2. How do I fix the IMAP authentication problem in Thunderbird with Office 365?

Ans: When Thunderbird shows an “authenticated but not connected” IMAP error, first update the application, then disable IPv6 from Configuration Editor → network.dns.disableIPv6 → set to True, and restart Thunderbird. If the error still appears, the MacSonik Thunderbird Backup Tool can help you migrate Thunderbird mailboxes directly to Office 365 without needing manual IMAP authentication.

Q3. What are the correct IMAP and SMTP settings for Office 365 in Thunderbird?

Ans: To configure Thunderbird properly with Office 365, use these settings:
– IMAP Server: outlook.office365.com | Port: 993 | Encryption: TLS
– SMTP Server: smtp-mail.outlook.com | Port: 587 | Encryption: STARTTLS

If Thunderbird still doesn’t sync correctly, the MacSonik Thunderbird Backup Tool offers an automated alternative to directly migrate emails to Office 365 using secure authentication.

Q4. What if Thunderbird still doesn’t work with Office 365 after configuration?

Ans: If Thunderbird continues to fail after manual configuration, the best option is to use the MacSonik Thunderbird Backup Tool. It ensures direct migration of Thunderbird data to Office 365 without data loss or technical errors. The tool simplifies the process and guarantees a smooth connection between Thunderbird and Office 365 for all mailbox items.

About The Author

Abhishek Singh is a Technical Content Writer at Aryson Technologies, where he specializes in creating clear and insightful content on data migration, email management, and file recovery solutions. With a keen eye for detail and a passion for simplifying complex technical concepts, he helps users understand and navigate advanced software tools with ease.

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