It is even possible that you lose a few mails after trying out the above methods to fix the Mail app.

One of the major problems which you may face in the Mail app of Mac is that you may be losing the mails after the update.

This method allows you to restore the profile and all data associated with it on another computer or in another location. Choose the files you want to move once you've found them. Tap Select in the upper righthand corner. Open the Files app and make sure you're in the iCloud Drive folder. Once again, you'll head to the new Files app to move your iCloud Drive files around. Some times it’s required to find command location to use it as path is not set properly to /bin or /sbin or some other folder.