Conserve network bandwidth. Keep the message brief so that it doesn't clog up the network or the recipient's in-basket. When you reply to another e-mail, don't quote long passages from it. Retain the routing information from the top, as well as the signature block from the bottom. Use the subject line.
Readers like to be able to decide whether they want to read the message.
The subject line that appears on each incoming message helps them decide. Take some care with your writing. Although e-mail is informal, don't embarrass yourself by sending messages that you haven't proofread. Use uppercase and lowercase letters as you do in other forms of correspondence, and skip lines between paragraphs. Instead, use uppercase letters for emphasis.