Manual method is not a secure solution to import mbox data to MS Outlook. So if you want safe migration then use MailsDaddy MBOX to PST Converter. This is the best GUI based application and it supports 30 email client's MBOX data. You can export multiple MBOX data into PST format in few clicks as well as you can also merge these MBOX data into single and separate PST file formats
The tool compatible with all window and MS Outlook version whether old or new.

you may visit here to explore all steps: Convert MBOX to PST- using MailsDaddy MBOX to PST Converter