In this age of electronic correspondence, your email writing etiquette must be up to par or that first impression can be a dud. There are several components to electronic communication that can be glossed over in person. When you are face to face with someone, your expressions, tone of voice, and cadence, mean a lot. In email, it is more difficult to convey these subtle expressions. Make sure your subject lines make sense.
Busy people have busy email boxes.
Don't be cute or make them wonder what you are talking about. Be concise and informative. Email is not a formal means of communication-yet. Email is still a relatively informal means of communication. If you have something that is extremely important, use the old US Postal Service.