E-mail etiquette encompasses what is written, how it is written, and when. Also, because e-mail makes an instant answer possible, it makes it seem required. A month in e-mail feels like 20 years. A day feels like a week. Be more compact than a full-page letter.
Most people don t thoroughly read anything much longer than a memo, anyway.
Communication research shows that upper levels of management think their messages downward are more understood than they actually are. This applies to e-mail, too. Don t forget punctuation, capitalization, and spelling. His unique lower case writing style worked well for poetry, but is not appropriate for your client e-mail. Don t fall prey to this easy e-mail habit.