These allow any subscriber to send an email to the mailing list for distribution to all subscribers, in real-time without any screening.
Most lists are unmoderated.
There are more of these lists than there used to be because of problems with spam email, but they usually have fewer members and lower traffic, because it takes a lot of time for a moderator to read and check all of the incoming email on a high traffic list, so the size of a moderated list is somewhat self limiting. These lists are used to distribute information from a central source. Only one person or organization can send email to the list for distribution to all subscribers. These types of lists are often used by organizations to distribute information. A typical example is the NewsScan mailing list, which sends an email on developments in information technology to subscribers several times a week.