When using the email composition screen, the best practice is to send test messages. Ideally, there would be some way to tell if a particular email is a test or final email. This is common practice in other major communication products (eg MailChimp). To keep the email body identical, the easiest way to do this would be to put (TEST) in the email subject. So an email called "About church this Sunday..." would be "(TEST) About church this Sunday..." and the email body would be identical.