Thunderbird used to save its mails as MBOX format and Outlook used to keep its data in PST format. So if you want to import Thunderbird data in Outlook, then first you need to convert Thunderbird MBOX files to PST format and for that, I m suggesting you, use [http://example.com MBOX to PST Migration] tool which allows you to convert multiple MBOX files from Thunderbird to PST format along with accurate emails formatting and attached files.