Without going into too much detail, eSoftTools PST to MBOX Converter Software to Thunderbird. Outlook PST files can be easily converted to MBOX and software is available for all Windows platforms. Using the split options, you can divide large files into multiple small files. The software includes a trial version as well as technical support. You can convert Outlook PST files to MBOX files in the trial version. Technical support is available around the clock, seven days a week.