I recommend using specialised software to convert MBOX to PST files, such as the excellent eSoftTools MBOX to PST Converter Tool. MBOX to PST Converter tool is one of the most common and secure conversion tools for a variety of email clients, including Apple Mail, Thunderbird, Entourage, Pocomail, and others to EML, EMLX, MSG, OFFICE 365, HTML GMAIL, YAHOO MAIL and HTML.
Read more:- Convert MBOX to PST file
Read more:- Convert MBOX to PST file