I believe that using the eSoftTools PST to Thunderbird Converter Software to import Outlook PST files into Mozilla Thunderbird is the best option. With a few mouse clicks, it can import a pst file into Mozilla Thunderbird. It may also import multiple Outlook PST files into Mozilla Thunderbird. The software has provided a trial version without paying money. In the trial version, you can convert 25 items of every folder and technical support is also available here at any time.
For more information:- Import Outlook PST File to Mozilla Thunderbird
Import PST Files to Thunderbird
Well. the first approach is to set the outlook application as your default program. Continue with the procedures to import PST files to Thunderbird:
Go to the Start button, click on the Default Program, and then on Set Your Default Program.
Now Select Outlook from the Program and Click on the Set this Program as Default.
Then, click on the Display the Thunderbird Menu.
Go to the Tools option and then on Import.
Choose the Mail option or you can opt for the Import Everything option. Click on the Next option to proceed.
Now, you have to choose file type as Outlook, continue with the Next option.
At last click on the Finish button to complete the procedure of Import.
This may help you out, Jimmy Wick