We always should try to write concise yet comprehensive explanations and make an effort to make receivers well-understood. We should take good care of the following items. We should take care not to deliver to wrong people by mistaking the addresses. You should create a mailing-list instead. We should not write a long subject since it is hard to read.
Carriage return means end of line and null line expresses end of paragraph.
One line should be limited to 70 characters or so. It is very hard to read if you write a message on every other line or in a long line without folding. Especially long lines are trouble to cite. Some people write a message with indent but it is meaningless. Text is displayed differently on each machines, so even if the layout is excellent on your machine, it might not be so on other machines.