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Import MBOX to Thunderbird the Smart Way in 2025

Published By Mohit Kumar Jha

Approved By Admin

Published On August 23rd, 2025

Reading Time 7 Minutes Reading

You finally got your old emails out of Gmail, Apple Mail, or another client, but now they’re stuck in an MBOX file, and Thunderbird won’t allow you to open it. That’s frustrating! The good news is, importing MBOX to Thunderbird in 2025 isn’t complicated with the right methods. This guide outlines how to import MBOX to Thunderbird via four reliable methods with step-by-step instructions.

Therefore, don’t worry, I’m here to guide you with the same. So, let’s know about some scenarios in which we need to move MBOX files to Mozilla Thunderbird.

Why Add MBOX to Thunderbird?

Exporting MBOX files from different clients, i.e. Apple Mail, Gmail, Eudora, and Opera Mail, is easy. But after exporting, it becomes inaccessible, unless you import it into Mozilla Thunderbird.

I personally prefer Thunderbird because it’s:

A free and open-source platform means you don’t need to buy a license like Office 365.
Works smoothly on Windows, macOS, and Linux.
Thunderbird natively support MBOX, unlike Outlook, which needs conversion to import MBOX to Office 365.
It supports add-ons, custom folders, and offline access, which makes it a go-to application for remote work.

Not only this, but when I import MBOX to Thunderbird, I was able to:

Access all my Gmail Takeout archives locally.
Restore old project emails that I had exported years back.
Keep a searchable offline copy of critical business communications.

I hope you clearly understand why we need to move our offline copies to Thunderbird, rather than Apple Mail or other clients. Now, the question is how to do so? I’ll give you the answer in the next section.

How to Import MBOX to Thunderbird?

Thunderbird does support MBOX natively, but here’s the catch: there’s no simple File > Open > MBOX option to add MBOX to Thunderbird. Don’t panic! I’ve four reliable options to do this task in minutes without losing data. Just carefully follow the instructions, and opt for any that suits your needs best:

#Method 1. ImportExportTools NG

The most practical and free solution is the ImportExportTools NG add-on offered by Mozilla Thunderbird itself. It works across Thunderbird’s latest versions 115 through 142 in mid-2025, including ESR 128, and makes importing straightforward.

So, you can opt for this without any doubt to import MBOX to Thunderbird (if you’re using the latest version) by following these steps:

Step 1. In Thunderbird, go to Add-ons and Themes, search for ImportExportTools NG, install it, and restart Thunderbird.

Step 2. Create a destination folder (optional): Right-click Local Folders > New Folder before importing to keep things manageable.
Step 3. Now, import the MBOX file, right-click Local Folders.
Step 4. Then, hit the ImportExportTools NG option, and click on Import mbox file to add MBOX to Thunderbird.
Step 5. Select Import directly one or more mbox files > pick your MBOX file.

Once imported, you can drag and drop emails or folders from Local Folders into your Gmail or IMAP account. For the same, you have to enable IMAP in Google Workspace, then you can access your data in it.

Limitations you faced with this add-on when you import MBOX to Thunderbird:

The add-on handles files up to ~4 GB each. Larger MBOX files need to be split first.
If your MBOX comes from Gmail Takeout, Thunderbird won’t restore labels automatically, even though Gmail adds them as X-Gmail-Labels headers. You’ll have to reapply labels manually after upload.

Therefore, this method is not suitable for large uploads and data hierarchy preservation. Still, you can use this if you have a small amount of data. Otherwise, move to the next solution.

#Method 2. Manual Import MBOX to Thunderbird via Profile Folder

If you’d rather not install add-ons, Thunderbird can read MBOX files directly from its profile folder. Here’s how:

In Thunderbird, go to Help, where you find More Troubleshooting Information > Open Folder to open your profile directory.
Now, select Mail/Local Folders/.
Copy your MBOX file into that folder. Rename it without an extension, e.g., Inbox instead of Inbox.mbox.
If a matching .msf index file exists, delete it.
Restart Thunderbird.

This method works, but it’s easy to make mistakes with filenames or indexes, so only use it to add MBOX to Thunderbird when necessary.

#Method 3. Preview Without Importing

Sometimes users just want to browse an MBOX without merging it into their active account. For that, use the Feeds account workaround:

Create a new Feed Account in Thunderbird.
In Account Settings, click Server Settings, and then Message storage, point the Local Directory to the folder that contains MBOX files.
Thunderbird lists each MBOX as a folder under that account.

This trick isn’t officially supported, but this way, you can look inside old MBOX archives.

#Method 4. Import MBOX to Thunderbird Via Cutting-edge Solution

Now, we have covered three manual methods. So, did you notice something that all of them come with some limitations, such as being time-consuming, error-prone, and bulk imports not supported. If yes, then you wonder about an alternative to manual methods.

That’s where I suggested a professional solution, i.e. SysTools MBOX to Thunderbird Importer to add MBOX to Thunderbird. It helps users to import large-sized MBOX data directly into Mozilla Thunderbird simultaneously, without needing any add-ons.

Download Now Purchase Now

This solution comes with advanced filters, which make the procedure smooth while keeping the data hierarchy maintained.

I’ve personally downloaded it for free and found:

No need for add-ons to be installed or complicated steps. The tool directly imports MBOX files into the Thunderbird profile.
You can import multiple MBOX files at once.
All your emails and subfolders stay exactly as they were.
Works with all Thunderbird versions (Windows & Mac).
Preserves attachments, metadata, and formatting.
24/7 Technical Support

Working Steps to Import MBOX to Thunderbird

After downloading the software, follow the steps given below:

Step 1. Open the utility, and click on Add File or Folder to upload the MBOX to it.

add file

Step 2. When you add the file, the tool shows a preview to verify.

preview

Step 3. You can leverage the date filter to import only relevant data.

date filter

Step 4. Now, the tool automatically configures Thunderbird profiles.

id's

Step 5. Select your profile and hit the Import button to add MBOX to Thunderbird.

import MBOX to Thunderbird

See, this is so easy! Within five quick steps, one can upload multiple MBOX files simultaneously. Additionally, the best thing is that you won’t face any limitations or errors throughout the import with this tool.

Moving Imports into Gmail or IMAP Accounts

If you’re restoring MBOX files to Gmail or another IMAP account, you don’t need to import MBOX to Google Workspace. Instead, you have to:

Set up your account in Thunderbird.
Import the MBOX into Local Folders using one of the methods above.
Drag the messages or folders into your Gmail/IMAP account.

Thunderbird uploads them to the server, but only the content, not the Gmail labels.

Author’s Verdict

In 2025, the easiest and safest way to import MBOX to Thunderbird is still with the ImportExportTools NG add-on. But, only if your files are less than 4GB. Otherwise, opt for the specified software (Method 4) to add MBOX to Thunderbird in bulk, while preserving the data hierarchy.