Are you looking a third party solution to import Outlook file into Thunderbird? Then you can try PST to MBOX Converter Tool is a unified solution that can easily import mail from Outlook to Thunderbird embedded all email attributes and attachments in exact form. This is an advance utility for users to import Outlook file into Thunderbird even when Outlook is not configured in system. All MS Outlook & Windows editions are supportable with this utility to perform the entire process of Outlook to Thunderbird. For understanding the softwares functionality you may use demo version of the software which allows you to export 25 mails from Outlook to Thunderbird. For bulk conversion you have to get license version of the product.