Types of Mailing Lists: Announcement vs. Discussion
There are two types of mailing lists available on Mailman: Announcement and Discussion.
Announcement mailing lists are intended to be used for announcements as the name suggests. Authorized senders will be allowed to send announcement emails to all subscribed members. (Information on how to add and remove admins for this purpose can be found under Removing or Adding an Admin)
Discussion mailing lists, on the other hand, are lists where all of the subscribed members are permitted to post on the mailing list.