A PST file is a data file that stores all your emails, contacts, calendar, attachments etc. ScanPST checks the internal structure of your PST file and if it finds any problems with PST then try to patch them up. You go to the Online PST Repair page, upload your broken PST file, and it handles the rest. It costs nothing, it is already available on your computer, and it clears up most of what goes wrong with a PST file. If it fails to repair the file then Stellar’s free online PST repair tool is a best alternative.