There is a tool called eSoftTools PST to MBOX Converter Software that can help you to know how to convert PST to MBOX. You don't have to pay to use it, and it converts pst files to mbox files for free. It works quickly and smoothly and gives you a live preview of emails and attachments in real-time. It's free to use, and you can convert up to 25 emails from each folder.
For more information:- Convert PST to MBOX for Free
