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
wholeclearSoftware 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. The application quickly deals with all large PST files and support their import into all MBOX supporting Windows and Mac-based applications. Users can easily export PST emails into MBOX with attachments. Read more :-
https://www.wholeclear.com/pst/mbox/