If you are looking for the best tool to migrate Thunderbird to Office 365, then I would like to recommend to you the best Third-Party software that efficiently converts MBOX to OFFICE 365, with the help of eSoftTools Thunderbird To Outlook Converter. It can convert Thunderbird to PST, MSG, EML, EMLX, NSF, HTML, OFFICE 365, GMAIL, and YAHOO. It can also export Bulk Thunderbird files to others file formats. It offers a free trial pack in which users can convert the initial 25 items from Thunderbird to Office 365 or others formats.
For more info- Migrate Thunderbird to Office 365
For more info- Migrate Thunderbird to Office 365