This module provides an interface for site admin to set up mailing list.
The point is that instead of using Drupal to create a mailing list, we'd better to use a third-party's mailing list service. Many websites provide mailing list. For example: both Google Groupd and Yahoo Group offer this service for free.
Most, if not all mailing lists have one common feature: a subscription email. Site admin provides a mailing list subscription email (usually something like firstname.lastname@example.org) and users can subscribe to that mailing list. Therefore, this module is service providers independent, it simply requires a subscription email.