You can use the Inbox Repair tool (SCANPST.EXE) to diagnose and repair errors in your Outlook data file. The Inbox Repair tool checks the Outlook data files on your computer to see if they're in good shape.
You might want to use the Inbox Repair tool in the following situations:
If you're using an Exchange email account, you can delete the offline Outlook Data File (.ost) and Outlook will recreate the offline Outlook Data File (.ost) the next time you open Outlook.
What happens after you repair an Outlook Data File?
In the Folder Pane, you might see a folder named Recovered Personal Folders that contains your default Outlook folders or a Lost and Found folder. Although the repair process might recreate some of the folders, they may be empty. The Lost and Found folder contains any folders and items recovered by the repair tool that Outlook can't place in their original structure.
Create new data file
You can create a new Outlook Data File and drag the items in the Lost and Found folder into the new data file. After you've moved all the items, you can remove the Recovered Personal Folders (.pst) file, including the Lost and Found folder. To create a new Outlook Data File, see Create an Outlook Data File.
Recover items from the backup (.bak) file
If you can open the original Outlook Data File, you might be able to recover additional items. The Inbox Repair tool creates a backup file with the same name as the original, but with a .bak extension, and saves it in the same folder. There may be items in the backup file that you might be able to recover that the Inbox Repair tool couldn't.
You can check the location of your Outlook Data Files in Outlook.