How to Fix Thunderbird Sending Duplicate Emails Problem?

  

Rollins Duke   
Published: June 9th, 2026 • 9 Min Read

Blog summary: This blog explains the main reasons why Thunderbird sends email twice, including technical issues, user mistakes. Explains manual fixes and professional Thunderbird duplicate email remover tool to easily remove duplicate emails without data loss.

You are here because your Thunderbird sending duplicate emails and you want to learn and solve the issue of Thunderbird duplicate emails problem. Then stay tuned with this blog to understand the reasons behind this problem and effective methods to fix the Thunderbird double emails sent and received problem.

Nowadays, millions of computer users use Thunderbird to send and receive emails. Thunderbird is an open-source email client which is available to use free of cost. Even Thunderbird’s easy-to-use graphical user interface and world-class security features force users to use it.

Why Does Thunderbird Sends Email Twice? (Technical Issue)

There are several reasons why Thunderbird may send duplicate emails. Some common causes include:

• Server Sync Issues: If Thunderbird does not sync properly with the email server, and because of this Thunderbird sends email twice. This thing usually happens when the server’s message unique identifier changes suddenly, causing Thunderbird to download or send the same emails twice.
• IMAP Folder Corruption: If IMAP folders are unexpectedly damaged or corrupted either on the server or inside Thunderbird, it can create syncing problems. Because of this, Thunderbird may show or send the email twice.
• Email Rules and Filters: Whether email rules or filters are not set perfectly in Thunderbird, they can accidentally trigger duplicate email actions. It is essential to confirm and make sure all the rules are correctly configured.
• Multiple Account Configurations: If more than one email account is set up in Thunderbird, or incorrect handling occurs between accounts can happen. In such cases, emails may be sent from the wrong account or seem to be sent multiple times.
• Add-Ons or Extensions: Some of the Thunderbird add-ons or extensions can interfere with normal email processing. This interference can result in Thunderbird duplicate emails. Users can try to disable or also try updating these add-ons to check if the issue gets fixed or not.
• SMTP Server Settings: If outgoing mail (SMTP) settings are incorrect, then Thunderbird may send the same email more than once. Users should always ensure their SMTP settings match the recommendations of their email provider.
• Send Later or Outbox Issues: When a user is using the “Send Later” feature or if the emails are stuck in the Outbox, duplicate sending can occur. This usually happens due to network or configuration issues, causing the same email to be sent multiple times.
• Imported Duplicates: Sometimes users open MBOX file in Thunderbird using the Import/ Export add-ons. But MBOX files may have duplicate clutter, and after completing the import process, your Thunderbird may be affected with duplicates.

Common Mistakes by Users That Cause Duplicate Emails

Thunderbird sends email twice can happen because of wrong settings, syncing issues, antivirus interference, misconfigured filters, POP3/IMAP conflicts, or accidental user activity like double clicks or shortcut errors.

Here are the common mistakes by users that can cause Thunderbird Duplicate Emails:

• Accidental Keyboard Shortcuts: Sometimes, when a user is typing an email, pressing the shortcut keys like Ctrl + Enter different times by mistake can send the same email not only once but many times.
• Overlapping Sent Settings: The email servers and Thunderbird both can try to save sent emails. If both are saving a copy of the same sent email, it may look like the email was sent multiple times.
• Incorrect Email Filters: If users do not set the email filter properly, then that can move or copy emails more than once into different folders, which can create Thunderbird duplicate emails.
• Accidental Double-Clicking: If the user clicks the “Send” or “Get Messages” button more than once quickly, Thunderbird may perform the same action more than one time, resulting in duplicate emails.

How to Stop Thunderbird Duplicate Emails Manually?

Above, we have discussed various reasons that cause Thunderbird to send emails twice. Hence, there are several solutions available to stop Thunderbird from sending duplicate emails. Use a solution depending on your problem, as mentioned below:

1: Disable Place a Copy in Sent Folder Method.

1. Start your Thunderbird email client.
2. Choose Tools >> Account Settings.
3. After that, Select Copies & Folders.
4. Uncheck Place a copy in Sent folder.
5. Restart Thunderbird and check for problems.

2: Check Server Settings Method.

1. Run Thunderbird on your computer.
2. Select Tools >> Account Settings.
3. Choose the Server Settings option to continue.
4. Ensure you have used the correct server settings i.e., Server Type, Server Name, Users Name, Port Number, and Security Settings.

3: Reconfigure Thunderbird Account Profile Method.

1. Go to Thunderbird’s profile storage location and create a Thunderbird backup.
2. Select the Thunderbird Account Settings >> Account Actions.
3. Click the Remove Account button to delete the configured profile.
4. Then, again, choose the Thunderbird Account Settings >> Account Actions.
5. After this, select the Add Mail Account from the options.
6. Enter your full name, email address, and password.
7. Click on the Continue button to proceed.
8. Configuration found in Mozilla ISP database, click Done.
9. Later, you can import backed-up data if required.

4: Delete Thunderbird POPSTATE.DAT File Method.

Thunderbird creates a popstate.dat file when a user sets up an email account using the POP settings. This file can keep track of emails, which have already been downloaded from the POP server, so Thunderbird doesn’t download them again. Sometimes, this file can get corrupted for various reasons. The user may need to recreate the popstate.dat file to fix duplicate email issues in Thunderbird.

Follow the steps below to remove duplicate messages Thunderbird by deleting the popstate.dat file:

1. Close the Thunderbird client and ensure the hidden files view is enabled.
2. Navigate to the Thunderbird profile storage location and open the Mail folder.
3. Now explore the Local Folders and delete the popstate.dat file.
4. Start Thunderbird client for recreating the popstate.dat file automatically.

Note: If your system is affected by viruses, then please scan your PC to detect and fix malware problems. Thereafter, you can disable the antivirus program and check problem is fixed or not.

Why Users Should Not Rely Only on Manual Methods?

The manual methods can sometimes fix the basic issues in Thunderbird, but they are not always the perfect solution to process when the email duplication problem is serious or repeated.

Here are the common drawbacks of the manual method for problems like Thunderbird duplicate emails:

• Temporary Fix Only: The Manual methods may provide the only temporary fix, and the problem can return.
• Risk of Data Loss: Incorrect manual changes by users can sometimes lead to data loss or email loss.
• Not Fix Root Cause: The Manual methods can only work on particular settings or small issues, and they may not solve the root which Thunderbird duplicate emails.
• Time-Consuming: Some of the manual steps may be very lengthy, complex, and time-consuming, which can take a lot of time for users to fix the error.
• Requires Technical Knowledge: This manual method needs basic technical knowledge, so a user from a non-technical background can’t do this process.

How to Resolve Thunderbird Sending Duplicate Emails?

Here is a simple step-by-step guide to remove duplicate messages in Thunderbird:

1. Launch the software and use the automated option to add Thunderbird profile data.
   
2. Select the required Thunderbird mailboxes.
   
3. Use a mode to fix Thunderbird clutter within and across folders.
   
4. Enable advanced filters to remove duplicate emails by date, email address, and subject.
   
5. The tool automatically chooses the default destination path to store the resultant data.
   
6. Click the Extract button to start deleting available replica emails across the selected folders.
   

Key Features of Thunderbird Duplicate Remover Tool

Here are the main features of this advanced tool. With this, users can easily remove duplicate emails in Thunderbird:

• Few clicks solutions: Users can remove duplicate emails in just a few clicks. It saves user time.
• Bulk Operation: Users can delete duplicate emails from multiple folders or multiple emails at once.
• Data Accuracy: It detects using details like subject, sender, receiver, date, and message-ID. It avoids the chance of deleting important emails.
• Advanced Filtering: Let users to preview the emails and select only the duplicates they want to remove.
• Fast and Automatic Process: Users don’t need to do manual checking. This tool automatically scans and removes duplicates quickly.

Frequently Asked Questions

Q1: How do I stop duplicate emails in Thunderbird?

Ans: You need to check Thunderbird’s account settings and follow the above-mentioned steps depending on your problem. Thereafter, you can stop sending and receiving duplicate emails in Thunderbird.

Q2: Why is Thunderbird sending emails twice?

Ans: Due to multiple reasons, Thunderbird may send duplicate emails, some of the causes are mentioned below:

• Server syncing issues.
• Email rules and filter.
• Multiple account configurations.
• Wrong SMTP server settings.
• Imported duplicates.

Q3: How can I delete duplicate emails from multiple Thunderbird profiles at once?

Ans: While manual methods can delete duplicate emails from a single profile, doing multiple profiles will take a lot of time and effort, but still not at once. To handle multiple profiles at once, you will be required to use a professional tool, which will make it hassle-free and quick to perform.

Conclusion

In conclusion, we have discussed complete detailed information to resolve the Thunderbird duplicate emails problem. You can follow the mentioned instructions to resolve the Thunderbird sending duplicate emails problem. If you have any other doubts, you can feel free to contact our support team for more details.