1. Go to Messages and click Manage Messages.
2. Choose the message you would like to delete from the Manage Messages screen. (If the Subject of the message is not enough for you to determine if you're selecting the right message, click Preview to view the message.)
3. In the Action column on the left, click the link to Delete. This will delete your message.
   

If the link to Delete is not next to your message (if the only links are Preview and Clone) that is because you’ve already sent the message. You cannot delete a message that has been sent. You also cannot stop the delivery of a message that has been sent.