Why Thunderbird Import Failed Unexpectedly Without Reason?

Mark Regan
Published: June 11th, 2025 • 6 Min Read

Have you also encountered a situation where your Thunderbird import failed unexpectedly for some uncertain reasons? If yes, then we are here to assist you in fixing the Thunderbird import not working issue so that you can work efficiently with all the data that you require.

Therefore, Thunderbird is a globally used email client that has a bunch of advanced options to manage emails from different accounts swiftly. However, in some cases, when the user tries to import the files into it, the process gets stuck in between or fails, which restricts users’ productivity and also puts sensitive data at risk. Thus, to guide the users through this process to overcome the Thunderbird import not working issue, we made this complete blog post. It covers multiple aspects such as reasons, manual ways that may help, professional tools with accurate results, their pros or cons, and so on, which will surely provide a great alternative for this error.

What Led to the Thunderbird Import Failed Unexpectedly Situation?

There is no single reason that may end up with Thunderbird import not working issue as there is n number of situation which eventually creates this error. Hence, some of the most prominent reasons that led to the import failed unexpectedly Thunderbird are:

The user might have installed an outdated edition of Thunderbird, which limits the importing functions.
Enabling any third-party plugin during the Thunderbird import option also led to the Thunderbird import not working issue.
This issue also happens when the user is importing corrupt Thunderbird files, which the email client does not support at all.
In addition to that, if the Thunderbird profile is corrupted, then this issue also takes place and restricts the user’s work.
Also, a lack of storage space in the storage disk also fails the Thunderbird import process, as no more data can be added there.
Last but not least, if the folders that you are importing do not have the required permissions, then the error of Thunderbird import failed unexpectedly occurs.

How to Fix Thunderbird Import Not Working Issue?

There are multiple indirect ways that users have tried, and this helped them to eventually get free of the error of Thunderbird import failed unexpectedly. Thus, get a quick look at them below:

1. Update Thunderbird Version

Run Thunderbird and click on the menu icon.
Select the Help button and choose About Thunderbird.
Now, from the pop-up window, download the updated version, if available.
Once done, restart Thunderbird and try to import files into Thunderbird.

2. Use the Thunderbird Safe Mode

Firstly, close the running Thunderbird completely.
Once done, press the shortcut key Windows + R.
In the available field, type thunderbird.exe -safe-mode.
Then, hit the Enter key.
Now, in the pop-up dialogue box, click on Continue in Safe Mode.
Next, click on Tools and choose the Import option.
And, this is one of the best ways to run Thunderbird in safe mode by disabling all the third-party extensions, which may lead to the Thunderbird import failed unexpectedly error.

3. Delete the .msf Index File Using PowerShell

First of all, close Thunderbird completely.
Now, press the shortcut key Windows + X and select Windows PowerShell (Admin).
Once done, paste this command there.
“Get-ChildItem -Path “$env:APPDATA\Thunderbird\Profiles” -Recurse -Filter *.msf | Remove-Item -Force”
Wait a minute to let the MSF file delete successfully.
After this, restart Thunderbird like always and try to import files.
This is also a prominent way to fix the Thunderbird import not working issue.

Drawbacks of the Manual Way

Very lengthy and complex to follow for non-tech users.
These ways are prone to error, which puts the data at risk.
Consumes a lot of user time and energy.
Has no guaranteed results to fix the import failed unexpectedly Thunderbird.

How to Resolve the Thunderbird Import Failed Unexpectedly Issue?

It is possible that even after doing all the above-given conventional solutions, you still can’t fix the Thunderbird import failed unexpectedly error. That is why all the professionals suggest getting an automated solution such as BitRecover Thunderbird Import Tool, which gives 99.9% accurate results with minimal effort and resource consumption. It is tried, tested, and recommended by experts to bulk import files in Thunderbird without any hassle. The quick and simple steps of this tool are:

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Launch the mentioned tool on your device.
Now, click on Select Files or Select Folders to choose data to import.
Next, browse and pick the saving location.
Click on Convert to import MBOX to Thunderbird swiftly.
At last, start Thunderbird to check the fix of the Thunderbird import failed unexpectedly.

Features of the Professional Tool

There are numerous features that make the pro solution better than any conventional way, and some of the best ones that you must know are:

This software supports bulk data to import directly into the Thunderbird profile without any glitches or obstructions.
It ensures complete data safety in terms of attached attributes, content, and layout.
The mentioned tool fixes the Thunderbird import not working issue and other similar errors effortlessly.
The best thing about this solution is that it supports all mailbox extensions, including .mbs, .mbx, and .mbox.
It maintains a folder hierarchy even after the import, which helps in quick access and better data management.
Proved as a great alternative to Thunderbird ImportExportTool NG due to its advanced technology.

Conclusion

By the end of the blog, it is very evident that using the professional tool to fix the Thunderbird import failed unexpectedly error is the best solution. Thus, it takes care of the overall data and makes the process quick, reliable, and easy to follow for everyone. However, the conventional methods may be free, but have lots of limitations that put the data at stake. Last but not least, the professional tool also offers a demo edition, which is completely free of cost and allows the user to import 25 files from each Thunderbird folder.

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