The keyboard has a shift key. Don't use very long lines. Many mail readers cannot handle lines longer than 80 characters. If the system being used issues paragraphs without line breaks, output the message with line breaks. Don't use very short lines.
Short lines are also hard to read.
Use lines of 60 to 70 characters in length. Keep personal e-mail received from others private unless it is clearly labeled otherwise. Don't forward a personal e-mail message to a mailing list without the permission of the sender of the message. Don't assume something that is not there. If the message is unclear, ask for clarification before attempting to derive something that isn't stated.