If you want to convert PST files into MBOX format, I would like to refer PST to MBOX Converter. In this PST to MBOX Converter tool easily convert PST files to MBOX. This Software supports both ANSI & UNICODE file type. PST file also maintains Meta properties such as (to, cc, bcc, subject, from & attachment) after convert mail no data will be change. It is compatible with all versions of MS Outlook and Windows. Read more :-
https://www.wholeclear.com/pst/mbox/