How to Convert Thunderbird to PST - A Complete Guide

Converting Thunderbird to PST is easiest when you pick the right path. This guide shows the fastest manual method for small mailboxes, a bulk EML export workflow, and a converter option when you need to keep folder hierarchy intact.

Follow the Quick Answer below, then use the step-by-step methods with the screenshots on this page.

Method comparison (fast decision)

Note: See the New Outlook PST reality box above.

What transfers and what doesn’t

Before you begin (important)

• Classic Outlook is still the simplest for PST workflows.
• To export PST with SysCurve, Outlook (Classic) must be installed on the same Windows PC.

Source:Feature comparison between new Outlook and classic Outlook | Open and find items in an Outlook Data File (.pst)

Where are Thunderbird emails stored?

• Windows: %APPDATA%\\Thunderbird\\Profiles\\
• macOS: ~/Library/Thunderbird/Profiles/
• Linux: ~/.thunderbird/ (Profiles/ inside)

Inside a profile (often named default-release), look in Mail\\Local Folders\\ for local mail and ImapMail\\ for IMAP accounts.

Note: .msf files are index files. The actual mailbox data is typically the file with no extension (MBOX-style).

Source:Where Thunderbird stores user data

Thunderbird Local Folders: what you actually have

Local Folders live inside your profile under Mail\Local Folders\ and are stored as MBOX files without extensions. The .msf files are only indexes and do not contain the mail itself.

Two reliable ways to convert Local Folders:

• Bulk EML export (free): Use ImportExportTools NG to export folders to EML, then drag those EML files into Outlook and export to PST.
• Converter (best for large mailboxes): Use a Thunderbird MBOX -> PST converter to keep hierarchy and reduce manual steps.

Thunderbird MBOX vs Outlook PST (quick overview)

Thunderbird stores mail in MBOX files (one file per folder). Outlook uses PST, a database file that stores mail, attachments, and folder structure. Outlook cannot open MBOX directly, so conversion is required.

Why convert Thunderbird to PST?

• Job change or company requirement to use Outlook.
• Create an Outlook-friendly PST backup or archive.
• Migrate to Office 365 or Exchange with PST as the import format.
• Consolidate multiple Thunderbird folders into one Outlook data file.

Need a full migration that includes contacts and calendar? See Thunderbird to Outlook guide.

How to convert Thunderbird to PST?

Pick the method that matches your mailbox size and source type, then follow the steps below.

Method 1: Convert Thunderbird to PST using IMAP

This method is best when mail already lives on an IMAP server (Gmail, Outlook.com, Office 365). If the mail is in Thunderbird Local Folders, you must upload it to an IMAP mailbox (bridge) or use EML export or a converter. The steps below show a Gmail bridge example.

Requirements: Thunderbird and Classic Outlook installed.

Tip: If the mail is already on an IMAP server, skip the Gmail setup steps and go straight to adding the account in Outlook, then export to PST.

Step 1: Enable IMAP from Gmail

1. Log in to your Gmail Account.

2. Click the Settings Gear icon.

3. Click on the “See all settings” option.

4. Select the “Forwarding and POP/IMAP” tab.

5. In the “IMAP Access” section, choose the “Enable IMAP” option.

6. Click the “Save Changes” button.

Step 2: Generate App Password

1. Navigate to https://myaccount.google.com/ or click on your Profile icon and select “Manage your Google Account.”

2. Click the “Security” option and enable the 2-step verification.

3. Go back to the “Security” section, then type “App passwords” in the search box. After that, select the “App Passwords” option.

4. On the App Password screen, enter “Thunderbird and Outlook” in the app name textbox, and then click the “Create” button.

5. Copy the App password and paste it into Notepad, and then click the “Done” button.

Step 3: Configure Gmail in Thunderbird

1. Open Mozilla Thunderbird.

2. Navigate to the Menu and select the “Account Settings” option.

3. In the left sidebar, open the “Account Actions” dropdown and choose the “Add Mail Account” option.

4. Enter your Name, Gmail Address, and the app password. Check the “Remember password” box and then click the “Continue” button.

5. Select IMAP from the “Available Configurations” and click the “Done” button.

6. You will then see a screen confirming the successful creation of the account.

Step 4: Migrate Thunderbird emails to Gmail

1. Access your Gmail mailbox within Thunderbird.

2. Right-click on the Gmail mailbox and select “New Folder” to create a new folder.

3. Name the new folder and click “Create Folder” to confirm.

4. Review the folder listed in the left sidebar.

5. Navigate to the Thunderbird folder with the emails you want to transfer. Use Ctrl+A to select all emails if necessary.

6. Right-click on the selected emails and choose “Copy to” option.

7. Select the newly created folder in your Gmail mailbox as the destination.

8. This will copy the selected emails into your Gmail folder.

Step 5: Configure Gmail in Outlook

1. Launch Microsoft Outlook.

2. Go to the “File” menu and choose “Add Account.”

3. In the account setup window, enter your Name, Gmail address, and the previously created app password. Re-enter the app password for confirmation, then click the “Next” button.

4. After verification, Outlook will display a confirmation message.

5. In Outlook, go to the left-hand pane and find your Gmail mailbox.

6. Select the folder you created earlier. Outlook will then start downloading all emails from this folder.

Step 6: Export PST from Outlook

1. Open MS Outlook.

2. Click on the “File” menu, select “Open & Export,“ and then choose the “Import/Export” option.

3. Choose “Export to a file” and click the “Next” button.

4. Select “Outlook Data File (.pst)” and then click the “Next” button.

5. Choose the folders you want to export. Ensure the “Include Subfolders” option is checked, then click the “Next” button.

6. Use the “Browse” button to choose a destination for saving the PST file. Opt to exclude duplicate items. Finally, click “Finish” to complete the export process.

By following these steps, you should be able to successfully convert Thunderbird emails to PST format using IMAP.

Limitations

Multiple Configurations:

This method requires you to configure three separate applications (Gmail, Thunderbird, and Outlook), which can be confusing for less technical users.

Intermediate Steps:

Using Gmail as an intermediary adds extra steps, increasing the likelihood of errors during the process.

Gmail Account Requirement:

You must have a Gmail account, which may not be ideal if you prefer to keep your email data local or within your corporate domain.

IMAP Limitations:

IMAP syncs email data over the network, so issues like network instability, synchronization errors, or Gmail’s own restrictions (such as upload limits or storage quotas) can hinder the process.

Potential Data Loss:

There is a risk of missing or incomplete email data during the migration, particularly if attachments or certain metadata don’t sync properly.

Duplicate Emails:

The process might create duplicates, especially if the synchronization settings are not correctly managed.

Slow Syncing:

Uploading large volumes of emails to Gmail and then downloading them via Outlook can be time-consuming, especially with a slow or unstable internet connection.

Manual Verification Required:

After migration, you’ll need to verify that all emails, attachments, and metadata have been accurately transferred, which can be labor-intensive.

Account Credentials:

Generating and managing app passwords and ensuring the security of your Gmail account adds an extra layer of responsibility and potential risk if not handled correctly.

Sensitive Data Exposure:

Transferring sensitive emails through multiple platforms might expose data to intermediate storage vulnerabilities.

Method 2: Convert Thunderbird to PST using EML export (bulk)

Use this for Local Folders or smaller mailboxes when you prefer a manual route. Works in Classic Outlook.

Step 1: Export Thunderbird folders to EML in bulk

Export one folder at a time to preserve the same hierarchy in Outlook. Tip: ImportExportTools NG can export multiple folders (and subfolders) in one run depending on your version.

1. Install the ImportExportTools NG add-on in Thunderbird.
2. Right-click the folder you want to export.
3. Select ImportExportTools NG -> Export all messages -> EML format.
4. Repeat for each folder to keep the same hierarchy.

Step 2: Import EML into Classic Outlook

1. Create a folder in Outlook that matches the Thunderbird folder name.
2. Open the EML export folder in File Explorer.
3. Drag-drop EML files into Outlook in smaller batches (200-500).
4. After each batch, wait until Outlook finishes “Processing...” / indexing before the next batch.

If drag-drop fails: try smaller batches (50-100) or split by date.

Warning: Drag-dropping thousands of EML files at once can freeze Outlook; keep batches small.

Step 3: Export PST from Outlook

Use the Outlook export steps shown in Method 1 (File -> Open & Export -> Import/Export -> Export to a file -> PST).

Limitations

• Large batches can freeze Outlook; import in smaller sets.
• Folder hierarchy must be recreated manually unless you export/import folder by folder.
• Some metadata (read status, flags) may not transfer perfectly.

Thunderbird contacts and calendar (optional)

PST conversion focuses on mail. If you also need contacts or calendar:

• Calendar: Export calendars to .ics from Thunderbird and import into Outlook.
• Contacts: Export the address book to CSV or vCard (depends on your Thunderbird version), then import into Outlook.

Handle these separately from the mail conversion steps.

Method 3: Convert Thunderbird to PST using Thunderbird to PST Converter

Use the SysCurve MBOX to PST Converter when you need speed and full folder preservation for large Thunderbird mailboxes. It reads Thunderbird profiles or MBOX files and exports to PST, EML, MSG, and HTML.

Requirement: To create PST output, Microsoft Outlook (Classic) must be installed on the same Windows PC. Outlook does not need to be open during conversion.

1. Download and install the SysCurve Thunderbird to PST Converter.

2. Open the tool and click on the ‘Add File’ option.

3. Select the ‘Load Thunderbird Profile’ option and click on the ‘Upload’ button.

4. Once the loading is complete, select any folder to generate a preview. You can click on any item to view detailed information.

5. Click on the ‘Export’ option, choose the folders you want to export, and select PST as the export format.

6. Click on the ‘Browse’ button and specify the destination path where you want to store the PST file.

7. Click on the ‘Export’ button to initiate the Thunderbird to PST conversion.

8. Once the conversion is complete, click on the ‘OK’ button to finish the process.

After the conversion process, you can open the converted PST file in MS Outlook.

Other helpful features

• Convert Thunderbird emails to PST, EML, HTML, and MSG format.
• Preview Thunderbird email data.
• Support Thunderbird and other MBOX email clients.
• Maintain Folder Hierarchy.
• Automatically splits PST files over 5GB into manageable parts.
• Free Thunderbird to PST conversion for the first 10 items per folder.
• Support all versions of MS Outlook
• Compatible with Windows OS.

Advanced Conversion Tips and Best Practices

To ensure a smooth conversion from Thunderbird to PST, consider these advanced tips and best practices:

Always Backup Your Data First:

Before starting any conversion process, create a complete backup of your Thunderbird profile. This ensures that in case of unexpected errors, you can restore your original data without any loss.

Keep Software Up-to-Date:

Make sure that your Thunderbird, Outlook, and any third-party conversion tools are updated to their latest versions. This minimizes compatibility issues and improves overall performance.

Monitor Conversion Progress:

Especially when converting large datasets, keep an eye on the progress to quickly identify and address any interruptions or errors.

Consider Email Folder Hierarchy:

When migrating emails, maintain the folder structure to avoid confusion later on. Both the IMAP and dedicated Thunderbird to PST conversion methods typically allow you to preserve the original hierarchy.

Troubleshooting Common Issues

Despite the best preparations, you might encounter a few issues during the conversion process. Here are some troubleshooting tips:

Incomplete Email Transfer:

If you notice that not all emails have been converted, double-check the folder selections.

Slow Conversion Process:

Large email archives can slow down the process. Consider converting in smaller batches if necessary, or use a dedicated Thunderbird to PST Converter tool that is optimized for high-volume data.

Missing Attachments:

Verify after conversion that attachments are intact. If attachments are missing, re-export the affected emails and check if the issue is isolated to certain file types or sizes.

Authentication Issues with IMAP:

When using the IMAP method, ensure that your Gmail account’s settings are correct and that the generated App Password is used properly. Double-check the security settings on your Google account if connection errors occur.

Frequently Asked Questions

Sources

• Mozilla: Where Thunderbird stores user data
• Microsoft: Feature comparison between new Outlook and classic Outlook
• Microsoft: Open and find items in an Outlook Data File (.pst)
• Thunderbird add-on: ImportExportTools NG

The Final Word

Pick the method that matches your mailbox size and source. IMAP works for small IMAP accounts, EML export is fine for smaller Local Folders, and a converter is best for large mailboxes and preserved hierarchy. Always verify a sample of messages after export.

The Author

Deepak Singh Bisht

Content Lead |

Deepak is a dedicated IT professional with over 11 years of experience and a key member at SysCurve Software for the last 6 years. His expertise lies in email migration and data recovery, with a focus on technologies like MS Outlook and Office 365. He also works with SQL Server backup and recovery workflows and DBCC diagnostics in Windows environments. Deepak, who also delves into front-end technology and software development, holds a Bachelor's degree in Computer Applications.

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