Relying on the Read Receipt is a bad idea. It's entirely possible to configure the prepane view to display the message without marking it as read. So the user immediately views the message in the prepane view, dilligently implements the task the Exec request of them, and then deletes the email. The Exec gets a Deleted Not Read notification back, and explodes because his employee is deleting his mail without reading it (when in reality the employee did do what was requested).
Educate your Execs that relying on Read Recipts is a bad idea.