Then the mail is sent only to that person. The beauty of discussion lists is that a subscriber can have an open discussion with dozens or hundreds of people on a somewhat focused topic. The actual time of day or night does not matter. This is actually a good thing to do when first joining a list, because the new subscriber can be accustomed to the courtesies, topics, and procedures of the list. Some discussion lists are moderated by a human and others are not.
Most lists allow open posting of messages without screening, even when the list is moderated.
Most moderators are there to maintain the list civility and keep it on topic and on track with its mission. Other moderators may edit messages or combine related postings. Subscribing members of the list often are instructors who offer great teaching tips suggested resources. The National Institute for Literacy administers several discussion lists on topics related to adult literacy and learning. There are extensive archives of discussion threads on each list.