Do you have your other email accounts forwarded to Gmail? If you don't you should and just not have a copy left in your old mailbox. That might be the easiest way to avoid this issue.
Go to Home>Settings>Applications>Manage Applications
Click the Menu button and select "Filter"
Select "Running"
Scroll down to the "Email" application. Select "Clear Data"
(This is effectively the same thing as deleting the account and starting over, however when I tried to delete/recreate the account using the UI, it didn't work. After deleting the information through the Application Manager, it appears that my email is working now.)