There are two kinds of lists in use at MIT: Mailman lists and Moira lists. Both have pros and cons are serve different purposes. The following table should be useful in helping you decide which kind of list best serves your purposes.
|Can be maintained by multiple people
|Can be used as an AFS group
|Can be used as a group for wikis.mit.edu
|Can be moderated (limit who can post)
|Offers a "digest" format for subscribers
|Can be automatically populated by the registrar with class members
As you can see, Moira lists have some feature which Mailman lists do not and vice versa. Occasionally, it may be necessary to have two lists - a moira list to control access to an AFS locker and a Mailman for announcements.
For more information, please see http://ist.mit.edu/email-lists.