Situation: The old email keeps popup after tenant migration. Microsoft Edge shows sing in.
Resolution 1: Remove the old email address from Account, Email & account, and Access work or school.
Resolution 2: Open Credentials Manger to remove the old email address.
Resolution 3: Delete the old email password from Microsoft Edge by going to Settings>profiles>Password.
Resolution 4: Clear browser data by going to Settings>Privacy, search and services.
Resolution 5: Delete the old email address from Registry.