Exchange OST files are prone to corruption making them totally inaccessible. Mentioning some of the reasons responsible for OST file corruption may include Exchange Server crash, database corruption, Exchange Server downtime, accidental user account deletion, etc. Inbuilt tools like ScanOST.exe can assist you in repairing minorly damaged OST files. To repair severely damaged OST files, you need to use a third-party Convert OST to PST freeware.