Migrate Emails from Thunderbird to Outlook? (Step-by-Step Guide)

Outlook is widely used across personal and business environments. Microsoft says its platform serves more than 400+ million monthly active Outlook.com users. But moving an existing Thunderbird mailbox is not as simple as adding your email account to Outlook. Thunderbird stores messages in the MBOX format, while Outlook works with its own data formats, including PST.

So, how do you migrate emails from Thunderbird to Outlook without manually moving hundreds or thousands of messages?

Two cases, two ways. For a small number of emails, you can save Thunderbird messages as individual EML files and drag them into Outlook. For larger mailboxes, you can convert the Thunderbird MBOX file to PST using an MBOX to PST converter and then import the resulting file into Outlook. The second approach is generally more convenient because it reduces repetitive manual work and can preserve the mailbox structure more effectively.

In this guide, we’ll walk you through both methods, explain their limitations, and show you how to migrate Thunderbird emails to Outlook step by step.

Reasons to Migrate Emails from Thunderbird to Outlook

Mozilla Thunderbird is a free, open-source email client that you can use on desktop, Mac, or even Linux PCs. Yet, many users look for ways to migrate email messages to Outlook from Thunderbird. Here are some reasons for this:

• To comply with business requirements in case an organization has transitioned to Outlook from Mozilla Thunderbird.
• To easily access all the emails, contacts, calendars, etc., in Outlook on any device. Thunderbird works only on the configured machine.
• To safeguard user data and privacy by utilizing Outlook’s enterprise-grade security features like Advanced Threat Protection, MFA, etc.
• Outlook has a built-in calendar app for scheduling meetings and appointments. Also, it can be shared with other users.
• Outlook uses cloud storage for storing emails, contacts, and other mailbox data. Thunderbird relies on local storage.

What are the Methods to Migrate Thunderbird to Outlook?

Now, let’s see the following methods that should help you migrate emails from Thunderbird to the Outlook client. Follow them to the T because poor email migrations can break business systems.

Method 1: Save Emails from Thunderbird as EML Files

Thunderbird stores emails in an MBOX file, which the Outlook desktop client doesn’t support. However, it does support the EML file format. So, as a workaround, you can save emails as EML files. Then drag and drop them into Outlook as per the following steps:

Step 1: Save Emails to EML File

First, you need to export emails from Thunderbird to EML format. To do this:

• Create a new folder for the exported emails (.eml) files.
• Then, Launch Mozilla Thunderbird on your PC.
• Click on a mailbox folder from which you want to save email messages.
• Select all the email messages you want to save.
• Right-click on them and click on Save As.

Note: You can also save emails using the ImportExportTools NG add-on in Thunderbird.

• Browse to the save destination and click on Select Folder.

The selected email messages will be saved as individual .eml files at the selected path.

Step 2: Drag and Drop the EML Files into Outlook

Now move the saved EML files into your Outlook account by:

• Launch Outlook on your Windows PC.
• Create a new folder (Click on Folder in the menu bar and click New Folder).
• Open the folder where you saved Thunderbird emails in EML format.
• Select those files and drag and drop them into the new folder created in MS Outlook.

Before proceeding with this method, skim through its limitations:

• It is a lengthy and time-consuming process as you have to save emails from every mailbox folder separately.
• The mailbox folder hierarchy is not upheld as emails are saved as individual EML files.
• It only exports emails and not other mailbox items like contacts, calendars, etc.
• You can miss or lose an email while moving them manually to Outlook.

Method 2: Using an MBOX to PST Converter

You can use a powerful Thunderbird to Outlook converter to convert the emails exported as an MBOX file to the Outlook-importable PST format. After that, you can simply migrate the resultant PST file to Outlook.

Stellar Online MBOX Converter is a free web-based utility that you can use to accurately transform Thunderbird to Outlook PST format in 3 simple steps: Upload > Convert > Download. 

It is an online service that you can conveniently use on any web browser to convert MBOX files on a Windows, Mac, or Linux machine. If you have more files to convert, you can upgrade to its Premium edition, with which you can easily convert 5 MBOX files of ≤5GB in size.

Also, Stellar’s online MBOX to PST converter safeguards your mailbox data as well as privacy. The converted mailbox file is available to download for up to 3 hours (Free) and 24 hours (Premium) after the mailbox file conversion. Once the time limit ends, the file is deleted automatically from the servers.

Here are the steps to use this web-based utility:

• Go to the free online MBOX to PST converter page using any web browser.
• Click on Upload MBOX File.
• The ‘Create an Account’ dialog pops up. Click on Sign Up at the bottom and enter your email ID and password. Click Sign Up again.

• Now, click on the Upload MBOX File button again.

• The Open window will appear. Browse and select the Thunderbird file. Click on Open.

• Once it shows the File Uploaded Successfully status, click on Start Conversion.
• After the conversion is complete, you will see the File Converted Successfully.
• Now, click on Save PST File to save the output PST file on your system.

Another option to export Thunderbird to Outlook directly is by using Stellar Converter for MBOX. It is a powerful desktop application that you can use to instantly export emails from a Thunderbird file to an Outlook profile without altering the mailbox structure or folder hierarchy.

To verify the mailbox data integrity before exporting the mailbox data to its destination, you can preview Thunderbird emails and other items like:

• Embedded images
• Attachments
• Contacts
• Calendars
• Tasks

You can also use it to convert MBOX files from 17+ email clients, including Apple Mail, Gmail, Eudora, etc., to PST format. Moreover, you can save individual mailbox entities as MSG or EML files.

Let’s see how you can use this software to directly export Thunderbird to Outlook:

• Download, install, and launch Stellar Converter for MBOX on your Windows PC.
• The Select MBOX window will appear.
• In the dropdown menu, select the email client (Mozilla Thunderbird).

Notes:The software will automatically select the default location of the MBOX file.If Thunderbird is not installed, or you want to select another file exported from Thunderbird, click on the Select Identity button.

• Once you have selected the MBOX file, click on Convert.

• It will scan the selected MBOX file.
• Once the scan is complete, it will show all the file data. Select any item to preview and verify it.
• Then click on Save Converted File.

• You will see the Save File window. Choose the Export to Existing Outlook Profile option.

• The Select Outlook Profile and PST dialog box will pop up.
• Select the Profile from the given list and click Save.

Note: If you want to add MBOX file data to an existing PST file, you can do so by clicking the Append to existing PST option.

• The software will begin importing the file data into the selected Outlook account. Once completed, the Conversion Completed dialog box will appear.
• Click OK to complete the process.

Conclusion

In this guide, we explored a manual way to export Thunderbird to Outlook. We also looked at an efficient solution – a third-party tool that can directly help you migrate Thunderbird emails to Outlook profile/s. The manual method of saving email messages as EML files is tiresome and repetitive. Stellar Converter for MBOX, on the other hand, simplifies transferring emails from one email client to another.

Moreover, you can also use the online MBOX to PST converter by Stellar. It lets you easily convert Thunderbird to Outlook PST format for free. After the file conversion, you can import the resultant file into Outlook using its built-in Import/Export wizard.

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