eSoftTools Software converts PST to Thunderbird Without Outlook. Outlook PST files can be easily converted to MBOX, and software can support all Windows platforms. You can divide large files into multiple small files by using the split options. The software comes with a trial version and 30 days money back gaurantee. In the demo version, you can convert 25 items from each Outlook PST files to MBOX files. Technical support is available 24x7.