If you want to fix the error OST is not Outlook data file, I have a solution for this problem. Use of eSoftTools OST to PST converter software, you can simply resolve and fix the OST file in Outlook without any problem. It has multiple options like OST to PST converter options, recovery OST file option, Split PST file option, bulk conversion option and other options. Using the bulk conversion option, users can convert a bulk OST file in one time without any errors.