To repair a broken Exchange Offline Storage Table (OST) file efficiently, the most effective and reliable method is to delete or rename the damaged file and let Outlook rebuild it automatically from the Exchange server. Because an OST file is simply a local cache of your mailbox, removing it does not delete your real emails, which remain safe on the cloud or server.
You can resolve this issue using the native solutions below, ordered from most efficient to advanced recovery. Rebuild the OST File (Recommended)
This approach completely replaces the broken file with a fresh, error-free copy downloaded directly from your Exchange server.
Close Outlook: Ensure Microsoft Outlook and any related processes are completely shut down. Open Run: Press Windows Key + R to open the Run dialog box.
Navigate to Directory: Type %LOCALAPPDATA%\Microsoft\Outlook</code> and click OK.
Locate the File: Find the .ost file that matches your troubled email account.
Rename the File: Right-click the file and rename it by adding .old to the end (e.g., outlook.ost.old). This preserves the old file as a backup just in case.
Relaunch Outlook: Open Outlook again. It will automatically detect the missing file, connect to the server, and safely download a fresh copy of your data. Use the Microsoft Inbox Repair Tool
If you have data in the OST file that did not sync to the server yet, you can use the built-in Microsoft utility (scanpst.exe) to scan and fix internal corruption.
Repair Outlook Data Files (.pst and .ost) - Microsoft Support
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