Make test emails more obvious

A test feature is standard for any platform, but I wish it were easier to tell right away that an email is just that--not the real thing yet. Adding [TEST] to the subject line or making larger the optional text at the top of the email would help. My boss reviews most emails I send out, and although I always add "THIS IS A TEST" at the top of the email, it's quite small, and I don't want him to think I didn't run the message by him first. It's a small request but one that can't be too hard to implement.