One-to-Many Communication (Mailing Lists, NetNews)
Any time you engage in One-to-Many communications, all the rules for mail should also apply. After all, communicating with many people via one mail message or post is quite analogous to communicating with one person with the exception of possibly offending a great many more people than in one-to-one communication. Therefore, it's quite important to know as much as you can about the audience of your message.