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Thunderbird Backup Tool is a full-fledged utility that migrates your Thunderbird mailbox to Office 365, Gmail, IMAP, Hotmail, Zoho Mail, etc. Moreover, it also safely backup MBOX files to PST, PDF, EML, EMlX, MSG, CSV, TIFF, etc. You can split your large resultant PST file into small parts through the split resultant PST feature. Additionally, the utility allows you to save your email attachments separately. You can try the full-featured trial version of the software to analyze the performance. 

However, Here is an informative article to help to transfer Thunderbird to Outlook 365 is Migrate From Thunderbird To Outlook 365.  They will give you the most efficient manual methods to migrate the process easily.