A moderated mailing list requires each subscriber and message to be approved by the "owner" of a list. The owner of a moderated mailing list is the person designated to manage the users subscribing to the list and monitor all messages sent to the list. Every message sent to a moderated list must first be approved by the moderator before it can be distributed to the list's members.

An unmoderated mailing list has an "owner", but that owner does not have to approve subscribers, nor does the owner have any control of the messages sent to the list.