To migrate Thunderbird MBOX mailbox data into Exchange Server mailbox then try Thunderbird to Live Exchange Migration Tool. It is the most proficient utility that easily imports all the Mozilla Thunderbird data into the Live Exchange mailbox without losing any data. It has Auto-load and Searches Mail option that helps to add multiple TB MBOX files at the same time. The software maintains all the Meta-data properties, folder structure, and key elements after the complete migration. It performs with all versions of Windows OS. 

More info-  http://www.thunderbirdtooffice365.com/thunderbird-to-exchange.html