You can use this software this top-rated software to fix the error- OST is not an Outlook data file. Enstella OST to PST Recover Software is a great software for converting OST to PSRT. This software gives a spilt option for all users, they can convert big OST data to many small sizes of PST files. The software supports all the versions of MS Outlook and uses the preview option before the conversion. Try this free trial edition for all new users.

Read More - fix the error- OST is not an Outlook data file