goto options > Advanced Options > Service Book
Once there scroll through and find the old email address highlight them, hit menu and then delete. i had the same issue when i copied everything from my sprint curve to my vzw 8800.
So you want the actual emails to be deleted and never come back?
High light the last day -->press bb button-->select delete prior and all will be gone. Back up again and if you restore you will no longer have those emails and then hide the email folder and you will never know you have it.