How do I repair an Outlook PST file or recover an OST cache?

For classic Outlook on Windows, first identify the data file under File → Account Settings → Account Settings → Data Files. Close Outlook and make an independent backup before repairs.

1. PST files: Locate SCANPST.EXE in your Office installation, commonly C:\Program Files\Microsoft Office\root\Office16\ or its Program Files (x86) equivalent. The location depends on installation.
2. Open SCANPST, browse to the affected .pst, and start the scan.
3. If errors are found, keep the backup option enabled and choose Repair. Restart Outlook and review recovered folders, including Lost and Found. Recovery is not guaranteed.

OST files: These are normally synchronized caches, not standalone PST archives. For Exchange, Outlook can recreate the OST from the server. Before any cache/profile recreation, confirm server copies exist and back up or export unsynchronized mail and local-only folders, contacts, and calendars. For an IMAP mailbox or uncertain data, ask support for the appropriate recovery procedure rather than deleting the OST. Do not use the PST repair steps indiscriminately for OST files or new Outlook.