Electronic mailing lists are usually
fully or partially automated through the use of special mailing list
software and a group address that is set up on a server capable
of receiving email. Incoming messages sent to the group address
are processed by the software and distributed to all email
addresses subscribed to the mailing list. adapted from: http://en.wikipedia.org/wiki/Electronic_mailing_list
Groups are built around specific interests
Groups may be open membership (anyone who wants to join) or controlled.