ScanPST.exe is a free email scanning utility in Microsoft Office that is designed to scan through your Outlook’s PST File (which contains all of your emails) and check if there are any errors in it. Once errors are identified, ScanPST provides you options on how to fix them.
A typical error message from Outlook can be “The set of folders cannot
be opened. Errors have been detected in the file (path). Quit Outlook and all
mail-enabled applications and then use the Inbox repair tool (scanpst.exe) to
diagnose and repair errors in the file. For more information about the Inbox
repair tool, see Help.”
This video tutorial thoroughly explains the use of this free Microsoft utility.
If you still have problems with an Outlook .pst file after running scanpst.exe, try using Stellar Outlook Repair Tool.

there is a speical tool that can fix the 2GB size limit of the pst file.
It can be found in the microsoft download center.
@Jack – Quite true, I assume you are referring to the KB296088 article.
Does not work in all cases though.