If you want to import Thunderbird email to Office 365 file, use the most reliable tool that can convert multiple Thunderbird MBOX files at once without problem, which is the eSoftTools Thunderbird to Outlook converter tool. It has unique properties that allow users to easily import Thunderbird emails to Office 365 files without wasting time, and it can auto-load configured import Thunderbird emails for migration.

Get more info- Import Thunderbird email to Office 365