Consider using the MBOX Migrator Tool to convert MBOX files to MSG format. This tool supports conversion to various file formats such as PST, EML, PDF, HTML, EMLX, MHT, and TXT. It also allows for importing MBOX emails into various email clients, including Gmail, Yahoo Mail, Thunderbird, Outlook, AppleMail, OperaMail, MozillaMail, Eudora, Evolution, Sylpheed, Mulberry, and SeaMonkey. The tool also offers batch conversions of MBOX mailboxes, a Mail Filter feature for sorting emails by date, customizable naming conventions for the converted files, maintenance of folder hierarchy, and removal of duplicate email items.

If you want to convert an MBOX file to MSG, you should try this MacProTools MBOX Migrator Tool. It is one of the most reliable and secure programs for MBOX to MSG file formats. It is a full-featured software designed considering the modern user's requirements. It also converts MBOX to CSV and supports multiple file formats such as PST, PDF, EML, EMLX, MSG, HTML, and TXT on Mac OS.