Open discussion: anyone who is a member of the mailing list can submit information to be distributed to the entire group. In this way, a group discussion can take place.
Announcement lists: Another common type of Internet mailing list is the newsletter or announcement format, where a single writer (the list-owner or moderator) broadcasts a periodical e-mail to a willing audience (and the audience doesn't participate directly.) In most cases, the organization that runs the mailing list controls what information, is sent out.
Moderated forums/discussions: a hybrid of the two types above, where members of the group can submit information to be distributed to the entire group, but submissions need to go through an approval process before they are distributed.
Auto-responders: These are email "robots" which reply to any incoming electronic mail with a specific document. For instance, pricing@your-company.com could send back a product-pricing sheet to anyone who wrote to it.
