Use underscores for underlining. Remember a smiley does not negate an insulting remark. Include you name, or nickname, and your return e-mail address. Know the size of your message. As a rule, don't send messages over 100 Kilobytes.
Large attachments choke bandwidth.
Always use complete URL addresses. This allows your reader to double click on any complete URL address and they will visit the Internet address if their program accepts hyper-links. No one wants to see how many times someone else has read your message. Besides being childish and consuming time and bandwidth, sending chain letters can cost you your Internet privileges. Learn how to send BCC's, or how to send mass mail where the recipients are hidden.