People like to use e-mail because it is efficient and inexpensive. E-mail is taking the place of messages on a telephone answering machine because of its convenience. Although thought to be more casual, e-mail in a business setting demands that writers apply certain rules of good communication. Don't assume that the recipient knows what you are talking about. Explain yourself fully but efficiently.
More information is better than less.
Put yourself in the place of your recipient. Use proper, appropriate English. Some people have decided that capitalization, punctuation and grammar rules can be suspended for e-mail. As someone who has pride in every word you write, you should have a different attitude. Don't be too cute with text symbols.