Open OST files in your browser
The copy of an Exchange or Microsoft 365 mailbox that Outlook keeps on a computer. Open one right here, its folders as Outlook had them. Nothing leaves your device.
Or drop it anywhere on this page
What you'll see
Your mailbox opens as a folder in the file list, with a folder for each of its own, and each email you pick opens as mail apps show it.
- Every folder • Emails by date
- Emails, contacts and calendars • Each in its own viewer
- Search • Find any email by its subject
- Export • Save as ZIP or Extract all
About OST
Outlook keeps an OST for every Exchange, Microsoft 365 or Outlook.com account it syncs, so mail can be read offline. It's the same database as a PST, which Microsoft documents as MS-PST, and Outlook 2013 and later write it in 4 KB pages with packed blocks.
An OST only opens in Outlook on the computer and the account that made it. When an account is closed, a laptop is replaced or a profile breaks, the OST left behind can hold the only copy of mail people still need.
Filepeek reads the file in pieces and lists the mailbox's folders as Outlook had them. Each email opens in the mail reader with its attachments, contacts open as cards, and appointments and tasks open in the agenda. Save as ZIP or Extract all writes them out as EML, vCard and iCalendar files any app opens.
Outlook Offline Data File
.ost
Format
- MIME type
- application/vnd.ms-outlook
- Made by
- Microsoft
- Released
- 1997
Inside the file
- Folders
- Inbox, Sent Items and your own
- Emails
- With attachments, in HTML, rich text or text
- Contacts and calendar
- Contacts, groups, appointments and tasks
- Written by
- Outlook on Windows, for Exchange and Microsoft 365
Opens in every browser
Browsers download OST files, and Outlook opens one only on the computer that made it. Filepeek opens them in Chrome, Edge, Firefox and Safari.
- YouChromeOpens through Filepeek
- YouEdgeOpens through Filepeek
- YouFirefoxOpens through Filepeek
- YouSafariOpens through Filepeek
Questions
How do I open an OST file without Outlook?
Drop it on this page or choose Peek an OST. Its folders open in the file list, and each email opens when you pick it.
Can I open an OST from an old computer or a closed account?
Yes. Filepeek reads the file itself, so it needs neither the account nor the computer that made it.
Can I turn an OST into a PST?
Not into a PST. Choose Export, then Save as ZIP or Extract all, and every email is written as an EML file any mail app opens, contacts as vCards and appointments as iCalendar files.
Is my file uploaded?
No. The file opens inside your browser and never leaves your device.