OST viewer — open Outlook .ost files without Exchange
An .ost file is Outlook's offline cache of an Exchange or Microsoft 365 mailbox — and it normally opens only in the Outlook profile that created it. This page opens it right in your browser: read everything, then export to EML or MBOX to move the mail into any client. Nothing is uploaded.
Drag & drop your .pst / .ost file here
it is parsed in this tab — never uploaded
Your files never leave your device — everything is parsed locally in your browser.
Mailbox
License active ✓ Keep this key to yourself — abnormal usage will get it deactivated.Select a message to read it here.
- From
- To
- Cc
- Date
This message stores its body as RTF only — shown as plain text, so formatting is degraded.
How it works
Drop your .ost file
The offline cache from an old work account, a decommissioned laptop, an Exchange migration. Parsed locally in this tab — no Exchange account, no Outlook profile needed.
Browse the mailbox
The folder tree (Inbox, Sent Items, your custom folders) appears on the left; click any message to read it with its attachments. Calendar and contact entries show as items too.
Export to move the mail
An .ost cannot be turned back into a mail account by itself — export to EML (zip) or MBOX instead, then import into Thunderbird, Apple Mail or any other client. Free for the first 10 messages; unlimited with a license.
Simple pricing
The viewer and 10-message exports are free. A one-time license unlocks unlimited exports.
Free
$0
- Browse every folder, read every message — unlimited
- Single attachments download free
- Export the first 10 messages as EML zip, MBOX, PDF or CSV — unlimited times
- No account, no upload, no watermark
3-month license
$14.99 one-time · 90 days
- Unlimited exports — every message, every format
- Bulk attachment extraction (.zip)
- Cross-folder search
- 90 days from purchase, never auto-renews
By purchasing you agree to the Terms of Service and Privacy Policy. Full refund within 14 days if it can't handle your file.
Lifetime license
$29.99 one-time · forever
- Unlimited exports — every message, every format
- Bulk attachment extraction (.zip)
- Cross-folder search
- Pay once, use forever — no subscription
- Support a small independent tool
By purchasing you agree to the Terms of Service and Privacy Policy. Full refund within 14 days if it can't handle your file.
Frequently asked questions
What is an .ost file?
Outlook's Offline Storage Table: a local cache of an Exchange, Microsoft 365 or Outlook.com mailbox, kept so you can read mail offline. It lives on the computer that ran Outlook — and it is locked to the Outlook profile that created it, which is why a stray .ost is otherwise unreadable.
How do I open an .ost file without Outlook?
Drag it into the box above. The .ost container is the same family as .pst, so this viewer parses it directly in the browser tab: folders on the left, messages in the middle, bodies and attachments on the right. No Exchange account, no Outlook, no upload.
Can you convert OST to PST?
Honestly: no — writing valid .pst files is a different, much harder problem, and this tool does not do it. What it does do is usually what you actually need: export the .ost contents to EML files or an MBOX mailbox, which Thunderbird, Apple Mail and other clients import directly.
Can you open an orphaned or old Exchange .ost?
Yes — that is the main use case. Because parsing happens without any Outlook profile or Exchange connection, orphaned caches from deleted accounts open fine, as long as the file is not strongly encrypted (a strongly encrypted .ost stays tied to its original Windows account).
What's free and what does a license unlock?
Free, forever: opening any .ost, browsing every folder, reading every message, downloading single attachments, and exporting the first 10 messages in every format (EML zip, MBOX, PDF, CSV), unlimited times. A one-time license (3-month $14.99 or lifetime $29.99) unlocks unlimited exports, bulk attachment extraction, and cross-folder search.
Is my .ost uploaded anywhere?
No — never. The file is parsed by JavaScript inside your browser tab; no file bytes cross the network. Verify in the developer tools Network tab: only page loads, an anonymous usage counter, and license validation for paid users.