If you want to transfer your MBOX files into Outlook PST format then, try Shoviv MBOX converter tool which comes with advance features and makes your MBOX conversion more precise.
Download this tool from the following links:-
https://gallery.technet.microsoft.com/Best-MBOX-to-PST-converter-e009d3d4
https://download.cnet.com/Shoviv-MBOX-Converter/3000-2369_4-78237872.html