It would be helpful to be able to choose new emails, old emails or both for migration. I thought only new emails would be moved. Now I have all the old junk mail in my new account. How can I undo this?
I am sorry for the trouble! We are definitely looking into providing this option for migrations. Nevertheless, for the moment when you perform an email migration, all emails from your source account will migrate.
If you would like to remove the unwanted emails from your account, you should be able to do so without too much trouble by clicking on the right side of the label of your migrated email account, selecting “Remove label” and then “delete”.