MailsDaddy PST to MBOX Converter
To open any Outlook PST file into MBOX-based email client, download MailsDaddy PST to MBOX converter software and migrate single or multiple PST file to MBOX at once. This GUI application preserves email, attachments, properties, inline images and folder hierarchy in a converted mail format. User can also move data from PST to EML, MSG, HTML, MHTML & RTF format with this application. The software comes with the free demo edition and easily works with both ANSI and Unicode PST file without any hassle.
For more detail: https://www.mailsdaddy.com/outlook-pst-to-mbox-converter/