How to Repair and Recover a Corrupt OST File
An Outlook OST file can become corrupted after unexpected shutdowns, synchronization failures, storage errors, Outlook crashes, or other interruptions while mailbox items are being written. A damaged OST may cause Outlook to freeze, fail to synchronize, display data-file errors, or block access to mailbox folders and items.
If the original Exchange or Microsoft 365 mailbox is still available, Outlook may be able to rebuild the OST by creating a new local cache. When the original mailbox is unavailable, the OST holds unsynchronized items, or the file is too damaged for normal Outlook recovery, the mailbox items may need to be recovered independently.
EdbMails OST to PST Converter can scan corrupted OST files, preview recoverable mailbox items, and export the required folders and items to PST.
Quick answer: how to recover a corrupt OST file
- Check whether the mailbox still exists. If Exchange or Microsoft 365 is available, try rebuilding the OST first.
- Try Outlook repair or recovery options. Use the appropriate Outlook data-file or profile troubleshooting.
- Preserve the original OST. Avoid repeated modification of the damaged source file.
- Scan the corrupt OST with EdbMails. Preview recoverable folders and mailbox items.
- Export the recovered data to PST. Select the required items and save them to Outlook PST.
Detailed methods are explained below.
An OST is Outlook's local offline copy of mailbox items for supported Exchange and Microsoft 365 accounts. Learn how Outlook stores mailbox items in an OST file.
Signs that an OST file may be corrupted
- Outlook cannot open the mailbox
- Outlook freezes while loading folders
- Repeated synchronization errors
- Inbox stops updating
- Folders or messages are missing
- Outlook data file cannot be accessed
- The set of folders cannot be opened
- Errors have been detected in the OST
- Outlook repeatedly crashes during synchronization
Common Causes of OST Corruption
- Unexpected system shutdown
- Outlook crash during synchronization
- Storage or disk errors
- Interrupted synchronization
- Malware or file-system damage
- Outlook/profile problems
- Improper manipulation of the OST file
Repair Method Hierarchy
Method 1 - Rebuild the OST When the Server Mailbox Is Available
- Close Outlook.
- Locate and rename/remove the damaged OST as appropriate.
- Reopen/reconfigure the mailbox.
- Let Outlook create a fresh OST and synchronize.
Important warning: rebuilding only restores data still present on the server. Locally stored or unsynchronized OST-only data may not be restored.
Method 2 - Use Microsoft Outlook Data-File / Profile Troubleshooting
Microsoft Outlook includes a built-in Inbox Repair tool, SCANPST.EXE, that checks an Outlook data file for errors and can fix minor ones. Microsoft recommends backing up the data file before running it, since the tool cannot analyze data stored in an Exchange mailbox itself, only the local file.
- Back up the OST file, then exit Outlook.
- Browse to C:\Program Files (x86)\Microsoft Office\root\Office16 (Outlook 2016/2019; check your Office install path for other versions).
- Open SCANPST.EXE and select Browse to choose the data file to scan.
- Choose Start to begin the scan.
- If the scan finds errors, choose Repair to fix them.
- Start Outlook with the profile associated with the file you just repaired.
The Inbox Repair tool can only fix minor issues, and Microsoft's own documentation frames it around .pst files, though the same tool is commonly pointed at .ost files too. See Microsoft's official Repair Outlook Data Files (.pst and .ost) guide. It is not designed to recover severely damaged or orphaned OST files.
Method 3 - Recover the OST When Normal Outlook Repair Is Not Enough
- Original mailbox no longer exists
- OST contains unsynchronized local data
- Outlook cannot mount the OST
- OST is also orphaned
- Corruption prevents normal synchronization
- Specific mailbox items must be recovered independently
Rebuild vs Recover Decision Table
| Situation | Recommended action |
|---|---|
| Mailbox still available on Exchange or Microsoft 365 | Rebuild or resynchronize the OST |
| OST contains only server-synchronized data | Rebuild the OST |
| Original mailbox deleted | Recover local OST data |
| Outlook profile deleted | Recover the OST if required |
| Unsynchronized local items may exist | Preserve and recover the OST |
| OST severely corrupted | Recover readable mailbox items |
| OST is orphaned and corrupted | Independent OST recovery |
| Exchange Server or database unavailable | Recover local OST if necessary |
Recover a corrupt OST with EdbMails
- Step 1 - Launch EdbMails
Select OST Recovery and Migration, then choose OST to PST.
- Step 2 - Select the Corrupt OST
Browse to the damaged .ost file.
- Step 3 - Scan and Preview
Check recovered folders, emails, contacts, calendars and attachments.
- Step 4 - Select Required Mailbox Data
Choose the full mailbox or selected folders/items.
- Step 5 - Export to PST
Start export and verify the conversion report.
What Can Be Recovered from a Corrupted OST?
- Emails
- Attachments
- Contacts
- Calendars
- Tasks
- Notes
- Journals
- Folder hierarchy
- Supported message metadata
Corrupt OST vs Orphaned OST
| Corrupt OST | Orphaned OST |
|---|---|
| Internal file/data damage | Original mailbox/profile relationship lost |
| May still be linked to an active mailbox | Usually disconnected from the original account |
| Rebuilding may work if server copy exists | Rebuilding may not restore old local OST data |
| Recovery needed when local data is inaccessible | Recovery needed when mailbox/profile is gone |
When Rebuilding Is Better
If the Exchange or Microsoft 365 mailbox is healthy and contains all required data, rebuilding the OST is usually preferable because the OST is a local cache. A dedicated recovery tool is most useful when local OST data cannot be restored from the server, when the mailbox/profile is unavailable, or when the damaged OST contains information that must be extracted independently.
Classify the Problem Before Repairing the OST
Before attempting repair, identify whether the issue is related to synchronization, Outlook profile configuration, storage problems, or actual OST data corruption. The correct approach depends on whether the original mailbox is available and whether the OST contains data that exists only locally.
| Observed condition | Likely category | Recommended first response |
|---|---|---|
| Outlook is temporarily offline or folders are not updating | Connectivity or synchronization issue | Check account, service and synchronization status before changing the OST. |
| Only one Outlook profile fails | Profile or configuration issue | Test the profile and preserve the OST if it may contain unique data. |
| Mailbox is healthy and complete on the server | Replaceable local cache issue | Create a new OST and allow Outlook to synchronize again. |
| File produces read errors or cannot be copied | Storage-level issue | Preserve the source and work from a protected copy. |
| Mailbox/profile is unavailable or OST contains local-only data | Recovery scenario | Evaluate the OST contents and export recoverable mailbox items. |
Document the Recovery Result
- Record the original OST filename, size and working-copy location.
- Note whether the file was active, orphaned or damaged.
- Save scan and export reports for reference.
- Verify recovered folders and item counts after export.
- Keep the original OST until the recovered data has been validated.
Frequently Asked Questions
How do I know if my OST file is corrupted?
Can Outlook rebuild a corrupted OST automatically?
Can ScanPST repair a corrupted OST?
Can I recover a corrupt OST if the Exchange mailbox is deleted?
Can I convert a corrupted OST to PST?
What if the OST is both corrupted and orphaned?
Can I preview mailbox items before recovery?
Should I try Outlook's built-in repair before using third-party software?
Why doesn't ScanPST.exe fix OST corruption the way it fixes PST files?
Can a corrupt OST still be opened in Outlook at all?
Does OST corruption cause permanent data loss?
What are the most common causes of OST corruption?
