How to Bulk Import Old Emails to Thunderbird Efficiently?

Rollins Duke
Published: August 8th, 2025 • 6 Min Read

If you are a Thunderbird user, have multiple old emails in your system, and are now seeking a reliable solution to safely import old emails to Thunderbird, then this is the right page for you. Here we are going to cover everything from the possible reasons or benefits behind doing this to the best solution for how to add old mail to Thunderbird efficiently.

So, there are times when we save our important emails locally, and when it becomes a pile, we wish to import old mails to Thunderbird so that we do not lose them permanently and can access their readable format whenever needed. Hence, to learn how to do this correctly and seamlessly, read and follow this complete guide till the very end.

What Makes Users Import Old Emails to Thunderbird?

The primary reason that makes a user search for how to add old mail in Thunderbird is to centralize all the emails on one platform.
Users also import mail to Thunderbird when they have old emails from another email client, and hence, they can successfully switch to the email platform.
Apart from this, some of the users also add old emails to Thunderbird for backup or archiving purposes.
Over and above the solution of how to add old emails in Thunderbird, allow the user to get offline access to the files.
Plus, by importing old emails in Thunderbird, users get the freedom to analyse, sort, and do advanced research in bulk emails, including the old and new ones.

Alert: To successfully and correctly import old emails to Thunderbird, the user has to make sure that their old emails are stored in MBOX file format, since Thunderbird accepts that only for healthy and bulk import of emails. If in case the emails are present in another file format, then they need to convert them to MBOX before importing them into Thunderbird.

How to Add Old Mail in Thunderbird Manually?

There are two different ways to conventionally import old emails to Thunderbird. However, they have some limitations that limit the users’ productivity. Still, to learn about them in brief, get a quick read at the below mentioned methods.

Method 1: Import Old Emails Using Thunderbird Add-ons

Run Thunderbird on your system and click on Tools.
Now select Add-Ons and Themes and search ImportExportTools NG.
Click on Add to Thunderbird to install it.
Once done, again select the Tools tab from the ribbon.
Then, click on ImportExportTools NG.
From the drop-down, choose Inbox MBOX files.
Further, select the old emails you want to import into Thunderbird and click Open.
And, with this, all your old emails in the Thunderbird acceptable file format will reflect in the local folder of Thunderbird.

Drawbacks: This method may not support email attachments, alter the image quality, or even lose data integrity. Thus, this solution of how to add old mail in Thunderbird is not so reliable. Also, the plugin mentioned here has lots of limitations, such as a restricted number of file imports, slow speed, and even corruption sometimes.

Method 2: Add Old Emails by Zipping Them

First of all, zip all the old emails that you have.
Make sure to use a professional tool to avoid data alteration.
Then, run Thunderbird on your device and click on the Tools tab.
Further, choose the Import option and then select the Import from a file option.
Now, navigate and click on the ZIP files of older emails.
Once done, hit the Next button.
After this, select the Start Import option to successfully import old emails to Thunderbird.

Drawbacks: This solution of how to add old mail in Thunderbird might look easy, but it has lots of restrictions, such as this Zip import feature is available only in the latest Thunderbird versions. Also, zipping bulk data often creates a blunder with data integrity. Not only this, but in this method, the Zip file size of older emails must be under 2 GB only, which is a complicated condition to swiftly fulfill.

How to Add Old Mail in Thunderbird Professionally?

The manual solution to import old emails to Thunderbird has lots of limitations and complications. That is why experts always choose a professional solution such as BitRecover Thunderbird Import Tool. It automatically fetches the old emails of the system that are saved in Thunderbird’s acceptable file format and seamlessly imports them into the Thunderbird account. There are some other advanced features of the solution as well, which make it the best choice to add old emails to Thunderbird in bulk without any data loss or corruption. The quick steps to use this tool are as follows:

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Run the tool on your system.
Click on the Select Files and Select Folders option to select the old emails.
Hit the Next button to choose specific old emails for a decluttered output.
Once done, click on the browse button to choose the saving destination of emails.
Finally, click on Convert to bulk import old emails to Thunderbird account.

Features of the Pro Tool

It has a dual selection mode to pick only the required old emails that the user wants to import in Thunderbird.
Supports all types of .mbx file variants, which boosts its versatility and makes it a better option to import MBOX to Thunderbird.
Has the ability to perform bulk actions and maintains data originality by importing attachments, header, footer, layout, signature, hyperlinks, etc., in their original way only.
Has advanced filter options that allow the user to make the output precise. Some of the filters are Date Range, Excluded Folders, Subject, From, To, etc.
Offers a demo edition as well, which is completely free of cost, and lets the user test the solution’s efficiency without getting the paid license.

Conclusion

In this complete blog post, we discussed the possible solutions of how to add old mail in Thunderbird. Thus, from the conventional ways to the professional tool, we shared the pros and cons of everything. Hence, if you have just 2-3 old emails, then you can follow the manual way, but if you have bulk old emails to import into Thunderbird, then blindly choose the automated utility mentioned above. It is fast, reliable, and extremely easy to import old emails to Thunderbird.

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