I recommend the excellent SysInspire MBOX to PST ConversionTool Software for efficiently converting MBOX to PST file formats. MBOX to PST Converter software is one of the most common and secure solutions for exporting data from a variety of email clients, including Apple Mail, Thunderbird, Entourage, Pocomail, and others. They've updated the features that are used to convert MBOX to PST files, such as stuff and envelopes. This software is available in free form. This app is available for download here.