Install and run PST to MBOX Converter on your system.
Go to the Browse button and add PST files to whom you would like to export.
Complete scanning and preview of PST files. Users can select items to export.
Now, choose MBOX format where you want to export the PST file.
Use the Browse button and set a location of your system to save the resultant MBOX file.
Finally, hit the Convert Now button to commence the conversion.