Please let me know if you know how to transfer PST files to Thunderbird without using Outlook. The eSoftToos PST to MBOX Converter Software is a simple way to convert PST to Thunderbird without worrying about Outlook migration problems. There are only a few more steps to complete. Each folder in a PST file should be exported as a separate MBOX file. Both of our customers have access to a free trial version. You will be able to use the trial version without charge.
For more information:- Import PST File to Thunderbird without outlook