To export data from a desktop-based email client (such as Thunderbird) to Outlook 365, the user needs an efficient conversion tool. If you want secure conversion, try MailsDaddy Thunderbird to Office 365 migration tool. This is the best GUI based application that allows a user to export single or multiple Thunderbird account emails to an Office 365 mailbox. It has the option of importing mailboxes into primary and archive mailboxes which makes the software more meaningful. Another is its security features that help import data in Office 365 without saving your login details.
For more detail visit: Migrate Thunderbird to Office 365
You can try this manual method steps by steps -
If this method does not work for you then to know other alternative methods you can check this blog here- https://www.stellarinfo.com/blog/migrate-thunderbird-to-office-365-account/
Moving Thunderbird mailbox to Office 365 account is a two step procedure.
First - Export Your Thunderbird Mailbox to PST format
Second - Import the Resultant PST into Office Account
Now it depend on you you to choose methods to perform these two steps either Manual Free Methods or Trusted Paid Software.
I personally used a single utility, which support to perform both steps at once. I also recommend you to use MBOX to Office 365 Migration Tool.
Moreover the software support to migrate all mail client MBOX file of any size. Also it supports to migrate contacts, calendars, notes, to-do, etc. along with emails.
Export Thunderbird mailbox to Office 365, I love to refer a professional third party tool, Kernel for MBOX to PST. The tool help users to Export Thunderbird emails to Outlook, Exchange and Office 365 environment in few steps. To know about the software step by step procedure, follow the given instruction at- https://www.nucleustechnologies.com/how-to/mbox/migrate-thunderbird-mbox-to-office-365.html
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