The free pst to mbox converter software is eSoftTools PST Recovery. This software converts PST files into many formats like MBOX, EML, EMLX, MSG, HTML, ZIMBRA, etc. It is free to download. If you can convert a pst file, it will always show the live preview of pst conversion also. This software runs on all Windows OS and it has no requirement to install MS Outlook on your computer. If you are not comfortable with this software you can claim your money back within 30 days.
Read More: - Convert PST files to MBOX format