Alert the user if there is no email address in the "To:" field when "Send" is clicked. Make this a preference setting if you must. I composed an email one night and I specified email addresses in the "Bcc:" field, but I left the "To:" field blank because I did not want to accidentally send it until I was sure I was finished. I forgot to enter a "To:" email address and the email was sent when I clicked the Send button! This resulted in a lot of problems since the intended "To:" recipient had no idea what I was talking about when I referenced the email.