If you want to convert your Thunderbird to Outlook 365 then you will go with this informative article Migrate From Thunderbird To Outlook 365. They will provide the most secure and effective manual solution to migrate the process. However, the manual solution has soo complicated. So, additionally, they will also provide a professional solution Thunderbird Backup Tool. The software is a fully-fledged utility that migrates Thunderbird to several email clients like Office 365, IMAP, Zoho Mail,  Yahoo Mail Hotmail, etc. It also saves your Thunderbird to PDF, PST, EMLX, EML, HTML, etc. Moreover, they utility allows you to save your email attachments separately. You can try the full-featured trial version of the software to analyze the performance.