Suppose the user cannot resolve the problem using the previous solution-checking procedure. In that case, the CloudMigration Thunderbird Email Backup Tool remains the tool of choice for transfer of Thunderbird data into the Office 365 email client. Also, the process is 100% effective and efficient. Thunderbird data could be modified into a variety of file forms, including MBOX, PST, etc., if the failure to connect Thunderbird with Office 365 occurred. There is also the choice of backing up Thunderbird emails to an external hard drive.

When there is some failure during the operation of Thunderbird with Office 365 emails, just read on for the best way of fixing it.

1. Download the Thunderbird Email Backup Tool into your PC.
2. Enter the profile from where you want to migrate the data.
3. Select from the tree structure mailbox Thunderbird Folder. Hit Next.
4. Now choose Office 365 email client from the saving options screen.
5. Sign In to Office 365 and use the software features if required.
6. Press on the Convert tab, and this will confirm the migration of Thunderbird data into Office 365.

Read More: https://www.cloudemailmigration.com/blog/thunderbird-not-working-with-office-365/