This means you must make sure you really want the message to go as you have written it. Most auto-replys will go to all members of the list. When sending a message to more than one mailing list, especially if the lists are closely related, apologize for cross-posting. If you ask a question, be sure to post a summary. When doing so, truly summarize rather than send a cumulation of the messages you receive.
Some mailing lists are private.
Do not send mail to these lists uninvited. Do not report mail from these lists to a wider audience. If you are caught in an argument, keep the discussion focused on issues rather than the personalities involved. The people who pay the bills get to make the rules governing usage. Be sure you check.