Follow Netiquette rules, including:

• Keep messages brief. Snip extraneous information, such as routing information, if you are replying or forwarding a message. If you need to write a longer, detailed e-mail, don't put important information at the end. Write a short summary at the beginning and then provide explanation.
• Don't send an e-mail unless you have something to say. For example, don't send an e-mail just to say you agree with an idea, unless that is why you were sent the message in the first place. Also, think carefully before you copy an e-mail to others. Does your boss really need that information, as well?
• Don't be sloppy with your writing. Read, edit and spell-check before you send an e-mail. Make sure your message is clear to the reader. While the informality of casual e-mail tends to be forgiving of mistakes, in the workplace these things matter! On the other hand, strive to be forgiving yourself, especially when corresponding with those for whom English is not their primary language. Correcting or pointing out errors publicly is definitely a no-no.
• Don't flame. Stay away from the keyboard when you're angry, and remember that problem situations are often better dealt with face-to-face.
• Use the subject line. It helps readers decide whether they need to review your e-mail at that very moment. Make your subjects specific and informative.
• Don't forward a message without the author's permission. Depending on the nature of the message, it can be unethical to forward a message to another person or to a public listserv.