How to Restore OST File
In short: To restore OST file data, know that for a live Exchange or Microsoft 365 account you replace the OST rather than repair it: close Outlook, rename the .ost, then reopen Outlook, which rebuilds a fresh OST from the server. There is no ScanOST tool any more, while ScanPST only fixes PST, not OST. If the account is gone and the OST is orphaned, you cannot rebuild it, so recover its data to a PST with a tool.
What restoring an OST really means
The word restore covers two very different situations, so picking the right one matters. If your email account still works, the OST is only a local copy of a mailbox that lives on a server, so you do not repair it, you throw it away and let Outlook build a new one. Nothing is lost, because the server holds the real mail. If instead the account is closed or unreachable, the OST is orphaned and holds the only copy, so now you must recover the data out of it. So the first question is simply whether your account still connects, then the two sections below handle each case.
Backup and Recovery Specialist, Corbett Software
“People hunt for an OST repair tool that does not exist, since ScanOST is long gone and ScanPST is for PST only. On a live account, just rename the .ost and Outlook rebuilds it from the server. Only an orphaned OST needs real recovery, which means pulling the data out to a PST.”
Live account: let Outlook rebuild the OST
For a working Exchange or Microsoft 365 account, this fixes a corrupt or misbehaving OST cleanly.
- Close Outlook completely.
- Open your local Outlook data folder at C:\Users\your-name\AppData\Local\Microsoft\Outlook.
- Rename the .ost file, for example to old.ost.bak, so Outlook cannot find it. Renaming rather than deleting keeps a fallback.
- Reopen Outlook. It builds a fresh OST and downloads your mailbox again from the server.
Give it time to finish syncing. Once the new OST is complete, you can delete the renamed backup.
Why there is no OST repair tool
This clears up a common wrong turn. Microsoft used to ship ScanOST to check OST integrity, but it removed the tool after Outlook 2010, so it does not exist on any current version. The other built-in tool, ScanPST, repairs only PST files and cannot touch an OST. So there is no official OST repair utility to look for. For a live account the rebuild above replaces the file anyway, while for an orphaned OST you move to recovery below rather than repair.
Orphaned or broken OST: recover the data
When the account is gone or the OST will not rebuild, the file holds your only copy and needs recovering into a portable format.
The Corbett OST to PST Converter reads an OST directly, including orphaned, inaccessible and mildly corrupted files, then recovers the mail into a PST that opens in Outlook. It keeps the folder structure, contacts and attachments, previews everything first, then can also save to PDF, EML or MBOX. A free demo edition lets you preview the recovered mail and runs on every edition of Windows.
- Install and open the tool, click Open, choose Email Data Files, then OST Files, then select your OST.
- Let it scan and preview the recovered folders and mail.
- Click Export, choose PST, apply any filter, then Save. Open the PST in Outlook afterward.
Frequently asked questions
How do I restore a corrupted OST file?
For a live account, close Outlook, rename the .ost, then reopen Outlook so it rebuilds a fresh OST from the server. For an orphaned OST, recover the data to a PST with a converter instead.
Is there a tool to repair an OST like ScanPST?
No. ScanPST repairs only PST files, while Microsoft removed ScanOST after Outlook 2010. There is no OST repair tool, so you rebuild the file or recover its data.
Will I lose emails if I delete the OST?
Not on a live account, since the mail is on the server and Outlook rebuilds the OST. Rename rather than delete to keep a fallback. An orphaned OST is different, so recover it first.
How do I restore an orphaned OST whose account is gone?
You cannot rebuild it, because there is no server to sync from. Use an OST converter to recover the mail into a PST, then open that PST in Outlook.
Where is the OST file located?
Under C:\Users\your-name\AppData\Local\Microsoft\Outlook. You can also check File, Account Settings, Account Settings, Data Files in Outlook for the exact path.
Does recovering the OST change the original file?
No. A converter only reads the OST and writes a new PST, so the original stays as it is while you get a recovered copy.