Corrupt Outlook data files usually result from abrupt shutdowns, oversized or aging PST/OST files, storage or file system errors, add-in conflicts, malware, and sync problems; the right fix depends on whether the file is a PST (repair with ScanPST or rebuild to a new PST) or an OST (delete and let Outlook re-sync), alongside profile repair and disk checks for persistent issues.​ https://kahkaham.net/read-blog/141029_what-causes-corrupt-outlook-data-files-and-how-to-fix-them.html