Repair corrupted Outlook .pst and .ost files with Inbox Repair Tool (ScanPST.exe), OST Integrity Check tool (Scanost.exe), OLFix and Fix It.

After recreating the OST file, remember to check for any missing mail items. If you found any, then use Stellar Converter for OST to recover them from the backup OST file.

2] Recreate the OST file An OST file (.ost) is an offline folder file in Microsoft Outlook used by account types like Microsoft Exchange Server.