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.
PST vs. OST explained
PST is a Personal Folders file used by POP accounts and archives, and corruption directly affects access to emails, calendar, contacts, and tasks stored only in that file unless you have backups.
OST is an offline cache for Exchange/Microsoft 365/IMAP; when corrupted, it’s typically safe to remove so Outlook can rebuild it from the server mailbox, assuming the server data is intact.
Why do Outlook files get corrupt?
Hard shutdowns, forced Outlook termination, or system crashes while Outlook writes to the data file can break internal indexes and tables that maintain folder and message structures.
Large/oversized data files, especially old PSTs that grow over time, are more prone to structural inconsistencies and truncation during repair attempts.
Disk bad sectors, failing SSD/HDD, and file system errors can corrupt blocks within PST/OST; malware and aggressive antivirus scans can also interfere with file integrity and locks.
Faulty or incompatible add-ins and flaky network connections can cause repeated sync failures and inconsistent item states that manifest as corruption symptoms.
Common warning signs
Outlook shows “Errors have been detected in the file … .pst/.ost” and may reference the local path under AppData\Local\Microsoft\Outlook, often accompanied by Event Viewer ID 2000 for OST issues.
Hangs on startup, frequent crashes, missing folders, or search not returning results point to damaged folder tables or message metadata inside the data file.
Quick decision tree
Using a PST? Repair with Microsoft’s Inbox Repair Tool (ScanPST), then validate data; if instability persists, create a fresh PST and move data across.
Using an OST? Close Outlook, delete the OST from %localappdata%\Microsoft\Outlook, and relaunch to re-download from the server; if it recurs, repair the profile and review add-ins/network/storage.
How to repair a PST with ScanPST
Close Outlook, run ScanPST.exe from the Office installation directory, select the PST, start the scan, and click Repair; allow it to create a backup before changes.
Microsoft documents that ScanPST validates and fixes folder and message properties, synchronizes recipient tables, recalculates sizes, and collects orphaned items into special folders, often requiring multiple passes until no errors remain.
After repair, mount the PST in Outlook and review “Recovered Personal Folders”; if the structure remains unstable, create a new PST and copy good data into it for a clean index.
When ScanPST isn’t enough
Severe or deep structural damage may exceed ScanPST’s scope, especially with very large PSTs; copying salvageable folders into a newly created PST helps rebuild consistent tables.
If critical items are still missing, consider specialized recovery utilities with caution, but always preserve a copy of the original file before any additional attempts.
How to fix a corrupt OST safely
For the “Errors have been detected in your .ost file” message, delete the affected OST in %localappdata%\Microsoft\Outlook and start Outlook to rebuild from the Exchange/Microsoft 365 server copy.
If corruption returns, recreate the Outlook profile from Control Panel or Account Settings and review connectivity, antivirus exclusions for OST paths, and add-ins that may lock or alter data during sync.
Profile, add-ins, and sync hygiene
Create a new Outlook profile when corruption loops persist; a fresh profile resets data file associations and service bindings that may be misconfigured.
Launch Outlook in Safe Mode to diagnose conflicting COM add-ins, then disable problematic ones that trigger sync errors or file locks leading to corruption.
Storage and file system checks
Run chkdsk and monitor drive health to fix file system inconsistencies and mark bad sectors, reducing the chance of fresh corruption during write operations.
Move Outlook data files to reliable local storage; avoid editing PST/OST from network shares or unstable external media to prevent partial writes and locking issues.
Import and permission pitfalls
If a repaired PST won’t import or throws access errors, verify NTFS permissions and ensure your Windows account has Full Control before trying again.
Keep the PST offline and closed by other apps during import or repair to prevent file locks and incomplete operations.
Best practices to prevent recurrence
Manage size: archive old mail, split large archives, and use Compact Now to keep PST/OST sizes in a safer, maintainable range.
Power and closure: shut down Outlook cleanly and use a UPS on desktops to avoid mid-write interruptions that damage tables and indices.
Keep your Office updated and exclude PST/OST paths from real-time scanning if your AV vendor recommends it, striking a balance between security and file stability.
Back up PST archives regularly; for server-backed mailboxes, rely on server retention and recovery options, while treating the OST as a disposable cache.
Step-by-step fixes at a glance
PST: Run ScanPST repeatedly until no errors; mount and validate; create a new PST and move data if instability persists; run chkdsk; rebuild profile if needed.
OST: Delete and rebuild from the server; if errors recur, recreate the profile, check add-ins and network reliability, and verify storage health and exclusions.
FAQs
Is ScanPST safe? Yes, especially when using the built-in backup option; always verify recovered content and consider migrating to a new PST for long-term stability after repair.
How many repair passes? Microsoft supports running ScanPST in multiple passes until a steady state is reached or no further errors are detected.
When to rebuild an OST? Prefer rebuilding whenever corruption is detected, since the master copy lives on the server for Exchange/Microsoft 365/IMAP accounts.
