Every user who wants to import Thunderbird files to Office 365 platform knows that this is not as easy as buttering bread, so a professional solution will be needed. To make it simple, secure and accurate, we recommend users to adopt the MailsDaddy Thunderbird to Office 365 migration tool. This device has been tested very well and the result is optimized. The tool is well coded so that it uploads all the information to the assigned mailbox without losing the format of the data in each migration.
The utility also has the option to move both primary and archive mailboxes with a fixed folder name. Due to the simple interface every user can use it and can choose it for unlimited migration. Its demo version has also been released which will allow you to convert the first 20 mails from each folder for free, which is quite enough as a test.
For more detail: https://www.mailsdaddy.com/thunderbird-to-office-365-migration/