Is there any manual method to add the MSG file into the Office 365?

Yes, there is a manual method to import MSG files into Outlook 365 successfully. To do so, you need to execute below steps:

1. Setup the Office 365 account on the Outlook Desktop.

2. On the Outlook ID right-click and create a folder.

3. Drag and drop the files into the newly created folder.

4. Now, you can see all of the files into the Outlook 365 account.