OST file support
Open OST files
without Exchange Server.
Upload Outlook offline data files (.ost) and search every email in your browser. No Exchange connection. No Outlook profile. No desktop software.
Why OST files are hard to access
OST files are tied to a specific Outlook profile and Exchange account. When the account is deactivated or the profile deleted, the OST file becomes an orphan that Outlook refuses to open.
When an employee leaves and their Exchange mailbox is deleted, their local OST file is the only remaining copy of their email. But without the Exchange connection, it's effectively locked.
Most OST recovery tools are expensive, unreliable, or require Windows. They often extract emails but don't provide a way to search the results afterward.
How it works
How Evermail handles OST files
Upload your OST file
Drag and drop the .ost file (or a .zip containing it). Evermail detects the format automatically. No special preparation needed.
Evermail converts and indexes
OST files use the same MS-PST format internally. Evermail walks every folder and message, extracts headers, bodies, threading info, and attachments, then indexes everything for search.
Search and browse
Full-text search across every email. Browse by folder, date, sender, or conversation thread. Download attachments. Export emails as EML or MBOX.
Technical details
OST support specifications
| File extensions | .ost, .ost.zip |
| Max file size (Free) | 1 GB |
| Max file size (Enterprise) | 100 GB |
| Exchange versions | Exchange 2003 through Exchange Online / Microsoft 365 |
| Orphaned OST files | Supported (no Exchange connection required) |
| Conversion method | MS-PST specification via XstReader engine |
Common questions
OST file questions
Can I open an OST file without Exchange?
Yes. Upload your OST file to Evermail and search it in your browser. Evermail converts OST files using the same engine as PST files. No Exchange Server or Outlook connection required.
What is the difference between OST and PST files?
PST files are user-created exports from Outlook. OST files are automatically created by Outlook as an offline cache of an Exchange or Microsoft 365 mailbox. Both use the same underlying MS-PST format. The key difference: OST files are tied to a specific Outlook profile and cannot normally be opened without the original Exchange connection.
Where do I find OST files on a computer?
OST files are typically stored at C:\Users\{username}\AppData\Local\Microsoft\Outlook\ on Windows. The filename usually matches the email address or Outlook profile name.
Can I recover emails from a deleted Exchange mailbox using the OST file?
Yes, as long as you have the OST file. Upload it to Evermail and all emails that were cached in the offline store will be extracted and searchable. This is particularly useful for employee offboarding scenarios.
Other supported formats
Unlock your OST files. Search them in minutes.
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