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Steps to Migrate Thunderbird to Office 365 account

Eric Simson  | Updated on June 18, 2020 | MBOX File   | No Comments   | 4 min read

Mozilla Thunderbird mail users are migrating to Office 365 for reasons like security, scalability, availability, collaboration, and affordable subscription-based pricing.

However, migrating Thunderbird emails to Office 365 or any other email client along with attachments is not an easy task. Firstly, Office 365 doesn’t support MBOX file type that is used in Thunderbird for storing mailboxes-comprising emails, attachments, contacts and calendars, etc. So, migrating Thunderbird mailboxes to Office 365 would first require converting all the data into a supported format such as Portable Storage Table (PST) or EML.

There are several methods available for migrating Thunderbird to Office 365 account. In this blog post, we will discuss them in detail.

Methods to migrate Thunderbird mailboxes to Office 365

As mentioned before, there are several methods of conversion. Let’s discuss those briefly below:

Method #1: Import EML Files to Office 365

Step 1: Save Thunderbird Email to Windows PC

  • First of all, create a new folder on Desktop.
  • Next, launch the Thunderbird application on the system.
  • After that, open the message folder where the emails that need to be moved from Thunderbird to MS Outlook are saved.
  • Then, select all messages.
  • Next, Right-click on the messages and select Save As option.
  • Then, Browse to the desktop folder and save the emails there.

Step 2: Import EML to Outlook 365

  • Launch the Outlook email application.
  • Then, go to the folder in Outlook where the Thunderbird messages will be saved.
  • Or, select Folder tab and select the New Folder option.
  • In the Create New folder dialogue box, set a name for the new folder.
  • Next, click on the OK button to migrate Thunderbird email to Office 365. Now, this folder will be shown on the left panel of the email application.
  • Next, click on the Folder to open its content on the center panel.
  • Finally, drag all the messages from Desktop folder to this folder in Outlook and your data will be migrated successfully.

Method #2: Forward as Attachments

  • Open Mozilla Thunderbird on a Windows PC.
  • Then, select the messages that need to be imported from Thunderbird to Outlook account.
  • Next, right-click on them and select Forward as Attachment.
  • This will open a new email window in which emails with be added as EML attachments.
  • Next, type in an email ID to migrate Thunderbird to Outlook 365.
  • Then, click on the Send button.
  • Finally, view the Thunderbird emails on Office 365 Mail App.
  • Verify the transfer process by logging into the O365 and opening each email one at a time through a browser in EML format.

Limitations of this approach

  • Migrates Limited Emails: The process to transfer Thunderbird emails to Exchange Online is not meant to move complete email folder containing over 1000 emails. It can only export limited number of conversations.
  • Lengthy and Time-Consuming: It would take a lot of time to move each email, one at a time, to desktop and then to Outlook. Forwarding hundreds of Thunderbird messages to Outlook 365 with large attachment files may take a lot of time.
  • Data Integrity Compromised: Often email formatting or SMTP header is changed for some emails during transfer.

The best alternative: For migrating Thunderbird to Office 365

The above discussed methods to migrate Thunderbird email to Office 365 would not be suitable for migrating a large amount of emails, attachments, contacts, etc. It’s better to use a professional software that specializes in exporting Thunderbird mailbox data to Office 365.

Stellar Converter for MBOX Technician is one of the most-preferred software tools widely used for migrating mailboxes from Thunderbird and other MBOX-based email clients to Office 365.

The trial version of the software lets you evaluate core functionality by way of scanning and preview of the converted emails, as follows:

free download
  1. Download, install, and launch the Stellar Converter for MBOX trial software
  2. On the software’s home screen, use the dropdown to select the source mail client to be converted to PST format
  3. On the same screen, click on ‘Select File’ to convert a single MBOX file. If you wish to convert multiple MBOX files in a folder, then click on ‘Select Identity Folder’
  4. Once the file is selected, click on ‘Convert’ to begin the scanning process
  5. When the scan finishes, you can check the preview of all mailbox components
  6. Click on the ‘Save’ button from the main menu to save the converted mails. You can save them to new or existing MS Outlook PST file, EML, MSG, RTF, PDF, HTML, as well as Office 365 file formats. Click on ‘Next’ after selecting an output format.
  7. If you select Office 365, provide your login credentials and click on Next to proceed
  8. Once the conversion is complete, you will be shown an appropriate message.

That’s it, you’re good to go.

Wrapping it up

Thunderbird uses MBOX file for storing mailbox data, which is not supported by Office 365, so, you’d need to first convert the MBOX file into a compatible format such as PST or EML. In this blog post, we shared a few methods to help you migrate from Thunderbird mail client to Office 365.

We outlined both manual and software-based methods for converting MBOX to PST or EML, all of which work fine from a technical standpoint, meaning, they do convert MBOX files to enable migration of mailboxes to O365.  

But, for all practical purposes—wherein high volume and variety of mailbox data is concerned—the software should be used. Why? Because as a business or an individual user you wouldn’t want to waste your time or get hassled performing the manual procedures while putting your mailbox data at risk of losing integrity. Using a specialized MBOX converter utility such as MBOX to Office 365 Converter by Stellar, automates the task with high precision, while minimizing the need for continual monitoring. 

The software is available for free trial which offers scanning and preview of the mailbox data. Once you’ve ascertained its effectiveness, you can then make an informed decision. It’s your call!