If you are looking to transfer your Thunderbird to Outlook 365 then you can opt for the Migrate From Thunderbird To Outlook 365. They will provide you with the best and most suitable manual method to accomplish the process. 

However, the manual method is so technical to use. So, in that case, you will choose a professional approach Mozilla Thunderbird Backup Tool. It is the most efficient and effective tool to save your Thunderbird mailbox to PST, PDF, EML, EMLX, MSG, CSV, TIFF, JPG, etc. They also safely migrate Thunderbird emails to several email clients and the cloud such as Gmail, Yahoo Mail, IMAP, Hotmail, iCloud, Zoho, Office 365, AOL, etc. Additionally, it is compatible with all versions of the Windows operating software. You can download the free demo version of the software to analyze the performance.