Open .ost Files Online — Free OST Viewer
Open OST File Online — Free & Instant
No signup required. Works in your browser.
📁 Drag & drop your file here
or click to browse • Max 100MB
✅ Free • ⚡ Instant • 🔒 Secure • 💻 No install
What Is a .ost File?
A .ost file is a email format known as OST. OST is an offline Outlook data file for Exchange accounts. This format is created by Microsoft and is widely used by professionals.
OST files contain structured email data that requires compatible software to open. With OpenAnyFile, you can read and archive .ost files directly in your browser without installing any software.
How to Open .ost Files Online
- Visit OpenAnyFile OST page
- Drag and drop your .ost file onto the upload area, or click "Browse" to select it
- OpenAnyFile automatically detects the OST format using magic byte analysis
- View, analyze, and read and archive your file contents in the browser
- Optionally convert to PST, EML, MSG or download
Software That Opens .ost Files
.ost files are primarily created by Microsoft. In the email space, you may encounter .ost files from third-party tools, online converters, or export functions. Regardless of the source, OpenAnyFile handles them all.
Open .ost on Different Platforms
- Windows: Use the original software or upload to OpenAnyFile for instant access
- macOS: Preview may not support .ost — use OpenAnyFile as a universal viewer
- Linux: Open-source alternatives exist, or use OpenAnyFile in any browser
- Mobile (iPhone/Android): OpenAnyFile works on all mobile browsers
Common .ost File Problems
Cannot be opened directly without Outlook.
Other common issues include: your OS not recognizing the file extension, the file appearing corrupted after download, or lacking the required software. OpenAnyFile bypasses all these issues with universal format detection.
Convert OST to Other Formats
OST files can be converted to 3 formats including PST, EML, MSG.
Related Email Formats
If you work with .ost files, you may also encounter these email formats:
- EML (.eml) — Open & convert .eml files online
- EML2 (.eml) — Open & convert .eml files online
- EMLX (.emlx) — Open & convert .emlx files online
- LDIF (.ldif) — Open & convert .ldif files online
- MBOX (.mbox) — Open & convert .mbox files online
- MHTML (.mhtml) — Open & convert .mhtml files online
- MSG (.msg) — Open & convert .msg files online
- MSG2 (.msg) — Open & convert .msg files online
- OST2 (.ost) — Open & convert .ost files online
- P7S (.p7s) — Open & convert .p7s files online
Popular OST Conversions
Frequently Asked Questions
What is a .ost file?
A .ost file is a email format called OST. OST is an offline Outlook data file for Exchange accounts.
How do I open a .ost file without installing software?
Upload your .ost file to OpenAnyFile. Our browser-based tool instantly detects and displays it — no downloads needed.
What program creates .ost files?
.ost files are typically created by Microsoft.
Can I convert .ost to another format?
Yes. OpenAnyFile converts .ost to PST, EML, MSG.
Is it safe to open .ost files online?
Yes. OpenAnyFile processes files in a secure, isolated environment. Files are automatically deleted and all transfers use HTTPS.
Can I open .ost on my phone?
Yes. OpenAnyFile works on all mobile browsers including iPhone and Android.