If you want your PST file to MBOX without losing any information then, you can install BitData PST Converter Tool. It is an excellent and amazing solution to convert files from PST to MBOX and other formats like PDF, HTML, DOC, ICS, CSV, JPG, BMP, IMAP, Exchange Server, Office 365, Yahoo, etc. With this tool, you can export multiple Outlook PST files to MBOX files with attachments in one go. One can try its demo version on any Win and Mac OS PCs.