When a list is moderated, all messages posted by non owners go to the moderators for approval. Once the moderators approve the message, it is posted through the list to everyone subscribed. A list configured to moderated-edit allows the list owner to make changes to a post before sending the message to the list subscribers. When a moderator is ready to approve a message he or she forwards the message back to the list address and the message is then posted to all the subscribers on the list.
Unmoderated lists have no moderators.
Messages posted to an unmoderated list are immediately distributed to all of the list's subscribers.