Import PST to Thunderbird With & Without Outlook – Complete 2025 Tutorial

Published By Mohit Kumar Jha

Approved By Admin

Published On August 7th, 2025

Reading Time 6 Minutes Reading

Thunderbird doesn’t support PST files, so if you’re switching from Outlook, importing your data isn’t possible until you convert PST to MBOX. I’ve done this recently, so I know the steps and solution to import PST to Thunderbird with or without Outlook. 

In this guide, I’ll share all my experiences and mistakes I often make during importing. So, read this guide completely without skipping any crucial sections to understand the dos and don’ts of this procedure.

Why Migrate PST to Thunderbird?

Recently, my organisation needed this migration, and maybe you relate to it too:

• Outlook comes with Office 365 Business Plans; on the other hand, Thunderbird is an open-source and free email client for data management.
• Compatible with Windows, macOS, and Linux. 
• For some reason, my organisation needed to pause the Microsoft 365 subscription. That’s why moving the Personal Storage Table to Thunderbird is necessary.
• It comes with a clean and simple UI, which makes it easy to handle by any skill level of users in the organisation.
• Thunderbird offers robust security measures to safeguard email data. By default, it can’t be synced with the cloud, so your data will be saved offline, which reduces the risk of hacking.

But Outlook stores everything in a PST file. Thunderbird can’t directly read PST unless Outlook is installed. So, let me explain to you what I found and how to migrate PST to Thunderbird effortlessly. 

How to Import PST to Thunderbird?

Moving Personal Storage Table to Thunderbird is not a straightforward procedure, as both email clients support different file formats to be imported, i.e. PST(Outlook) and MBOX(Thunderbird). 

However, I found some methods that help us import PST file to Thunderbird without Outlook or with. Further, I’ll share each with step-by-step instructions, but before following these prerequisites to migrate data hassle-free:

• Outlook is installed if you’re using Method 1.
• Install Mozilla Thunderbird on your system. If already installed, then verify storage space to import entire PST files simultaneously without any issue. 
• Ensure Office 365 backup best practices before any import process.
• Check that your PST is not corrupted. If you found any corruption, then use Microsoft’s Inbox Repair Tool to fix issues.

These are some common steps that help to import PST to Thunderbird smoothly. Now, this is the time to learn the solutions:

#Method 1. Migrate PST to Thunderbird Using Outlook

Thunderbird does not natively support importing PST files directly unless Outlook is installed and configured on the same system. Even then, this only works on Windows and with older versions of Thunderbird (pre-v78), because newer versions removed support for Outlook imports.

So, those who are using the latest version of both applications can move to the next solution. 

Users with Thunderbird (pre-v78) follow these steps:

#Step 1. Set Outlook as the Default Client

1. Open Control Panel, then go to Default Programs.
2. Set Outlook as the default mail app.

#Step 2. Set Up Thunderbird to import PST to Thunderbird

1. Open Thunderbird.
2. Select the Tools option, then click on Import.
3. Choose Mail, then hit Next.
4. Select Outlook from the list of email clients.
5. Thunderbird will import email data from Outlook.

Note: This solution will help to migrate PST to Thunderbird, including emails only, not contacts, and calendar data.

I repeat, this method only works with older versions of Thunderbird; newer versions don’t support importing a PST directly. Additionally, you need a live Outlook profile to import data directly from it, as any version of Thunderbird doesn’t support PST migration.

#Method 2. Convert PST to MBOX and Import PST to Thunderbird Without Outlook

If you don’t have Outlook installed on your system, but you’re having orphan PST files that need to be imported to Thunderbird. Then, the only option is to convert that data into MBOX format, which is supported by Thunderbird.

Follow the instructions to migrate PST to Thunderbird:

#Step 1. Use a Software

Opt for SysTools PST to MBOX Converter to convert PST emails into MBOX files that Thunderbird can read. Download this for free, and follow the steps for conversion:

• Open the solution, select the PST file, and upload it.
• Now, choose the export type as MBOX
• Hit the Export button.

Now, your data is converted to the MBOX format, and you can import PST to Thunderbird without Outlook.

Why choose this solution?

I recommend this solution because:

• It converts multiple PST files in minutes
• Maintains folder structure and attachments
• Has a user-friendly interface
• Converts even highly corrupted PST
• Outlook installation is not needed
• Converts both PST file types, i.e., ANSI & Unicode
• Compatible with Windows & macOS systems

#Step 2. Import MBOX to Thunderbird

1. Open Thunderbird.
2. Install the ImportExportTools NG add-on:
   • Go to Add-ons Manager, and press Ctrl + Shift + A.
   • Search and install ImportExportTools NG
3. Restart Thunderbird, and right-click on Local Folders.
4. Afterwards, hit the ImportExportTools NG option > Import MBOX File.
5. Choose to import MBOX files directly and select your converted file.

Emails appeared under Local Folders in a few seconds. Access them, and verify all the data is correctly migrated.

Common Mistakes I’ve Made

Here are some mistakes that make moving a Personal Storage Table to Thunderbird complex and time-consuming:

• I renamed PST to MBOX, which made the file inaccessible and showed an error to import PST to Thunderbird without Outlook or even with. So, don’t try to rename, just download the specified solution and convert the data to MBOX files simultaneously.
• I chose the manual method 1 to migrate multiple PST files, but it takes a lot of time. So, now I use an automated tool for bulk migration.
• I imported MBOX files, which are too large, around 3 GB, which slowed down my Thunderbird. So, split PST if your files are above 2 GB before converting. 

Additional tip: Use POP and IMAP settings carefully to migrate PST to Thunderbird hassle-free. Additionally, ensure the Office 365 migration checklist is followed to ensure zero data loss.

Author’s Verdict

If you have access to Outlook, the process is easier. Without it, converting PST to MBOX is your best option. Both the solution with step-by-step instructions are explained in this guide to import PST to Thunderbird smoothly.

If you asked me which solution is more appropriate, then I would say converting files to MBOX (Method 2), as it serves as a backup, and can be imported without Outlook.