If you have a bad email address in Recent Contacts, you can remove it, but the procedure is a bit tedious:

NOTE: You can delete a Recent Contact only in Notes 8.0.1 and later.

1. If you have not already, open your Contacts database; select Recent Contacts in the left-hand navigation pane.
    
2. Right-click on the contact you would like to delete, and select Delete from the context menu.
    
3. Select Trash in the navigation pane at left , and click Empty Trash in the action bar above the message list.
    
4. Send an email to yourself.
    
5. Restart Notes.