Many Outlook users struggle when they try to access OST data in Thunderbird because Thunderbird does not support OST files directly. This guide helps users understand why OST cannot be opened in Thunderbird, what challenges may occur during conversion, and how they can successfully import OST to Thunderbird using both manual and automated methods. It provides a simple, practical roadmap — from understanding the formats to applying reliable solutions — so users can move their mailbox data without losing emails, attachments, or folder structure.
- OST (Offline Storage Table) files are created by Microsoft Outlook when connected to Exchange, IMAP, or Microsoft 365 accounts. They store a synchronised offline copy of mailbox data and work only with the original Outlook profile.
- On the Other hand, Mozilla Thunderbird is a free, open-source, cross-platform desktop email client, storing its data in MBOX format. Due to this format incompatibility, Thunderbird cannot directly open OST files.
Below is a quick comparison to understand the difference between these two:
Comparison Between OST and Thunderbird:
| Features | OST (Outlook) | Thunderbird (Mozilla) |
|---|---|---|
| File Format | OST | MBOX |
| Used By | Microsoft Outlook | Thunderbird |
| Purpose | Stores offline Exchange/IMAP data | Stores local emails |
| Accessibility | Needs original Outlook profile | Can open on any Thunderbird setup |
| Encryption | Encrypted & profile-specific | Not encrypted by default |
| Direct Import Support | No | Yes (for MBOX only) |
| Supported Protocols | Exchange, IMAP, Microsoft 365 | POP3, IMAP |
| Readability | Not readable outside Outlook | Readable across many clients |
Before learning the methods, it is important to understand why users import OST to Thunderbird.
Reasons to Import OST to Thunderbird
Here are the most common reasons users switch from Outlook/OST to Thunderbird:
- To avoid Outlook licensing costs and use Thunderbird’s open-source environment.
- Moreover, to access orphaned OST files after uninstalling Outlook or deactivating Exchange accounts.
- For moving data from a corporate Outlook profile to a personal or cross-platform email setup.
- Similarly, Thunderbird allows multiple accounts, add-ons, extensions, and platform independence.
- Flexibility, lightweight performance, and support for multiple OS (Windows/Mac/Linux).
- In addition, there is a need to access old Outlook emails without relying on the original profile.
These reasons help users understand the most effective approach for ensuring a smooth and secure conversion process.
What are the Methods to Import OST to Thunderbird?
Because Thunderbird cannot open OST files directly, the conversion must be done through alternative techniques:
- Use a manual method (convert OST > PST > Import into Thunderbird).
- Use a professional automated tool (directly import OST to Thunderbird).
Both methods are explained below in detail.
Manual Approach to Import OST to Thunderbird
Thunderbird has no built-in option to open OST files. Therefore, the manual approach includes two major stages:
Stage 1: Export OST to PST using Microsoft Outlook
- Open Outlook > File > Open & Export > Import/Export.
- Choose Export to a File > Next.
- Select Outlook Data File (.pst).
- Choose folders to export from the OST mailbox.
- Browse a location > click Finish.
- The OST data is now saved as a PST file.
Stage 2: Import PST into Thunderbird
- Set Outlook as the default email app on your system.
- Open Thunderbird > Menu > Tools > Import.
- Choose Import from Outlook > Continue.
- Select emails, address book, or messages > Continue.
- Click Import to bring PST-converted data into Thunderbird.
Drawbacks of the Manual Approach
- Require access to the original Outlook profile and cannot handle orphaned, corrupted, or encrypted OST files.
- Need both Outlook and Thunderbird installed on the same system, limiting flexibility.
- Not suitable for bulk conversions and often fails to maintain folder structure.
- Time-consuming for large mailboxes and requires technical expertise.
- Higher risk of errors, missing data, or incomplete conversion.
How Professionals Export OST to Thunderbird?
To migrate OST to Thunderbird, the best way is to use a professional tool like Shoviv IMAP Email Backup and Restore. It is suggested to export the OST file data to the IMAP email server/ IMAP email account that is configured with Thunderbird. The software will migrate all data to your IMAP email server, and when you configure it with Thunderbird, your data will be accessed through Thunderbuird.
See What Does Shoviv IMAP Backup and Restore Offer?
- It can export email from PST, MBOX, EML, and MSG, like popular file formats, to any IMAP email server/account.
- Moreover, users can export data from any IMAP email client/server to various file formats.
- There are no limitations on the number of emails and data size to export.
- It allows for automating the backup process by scheduling.
- Shoviv IMAP Backup and Restore comes with various filter options so you can get only the desired email data.
- A free demo version of this utility is also available. Install the demo and evaluate this utility.
Gist of the Blog:
Various reasons initiate users to export OST to Thunderbird. There are a few manual ways to import OST to Thunderbird, but professionals always need an efficient and effortless way to handle their sensitive data. Shoviv Software offers a professional to handle it. A free demo version of the Shoviv IMAP Backup and Restore, and 24*7 free technical support is available.
