Maillist or Mailing List.

A (usually automated) system that allows people to send e-mail to one address, whereupon their message is copied and sent to all of the other subscribers to the maillist. In this way, people who have many different kinds of e-mail access can participate in discussions together.

Some mailing lists are simple "reflectors", redirecting mail sent to them to the list of recipients. Others are filtered by humans or programs of varying degrees of sophistication; lists filtered by humans are said to be "moderated". There are several programs to automate mailing list maintenance, e.g. Listserv, Listproc, Majordomo.

Mailing lists are easy to create and don't tie up a significant amount of machine resources (until they get very large). Thus, they are often created temporarily by working groups, the members of which can then collaborate on a project without ever needing to meet face-to-face. Business companies create their own mailing lists to inform customers about news and updates.

Requests to subscribe to, or leave, a mailing list should ALWAYS be sent to the list's "-request" address. This prevents them being sent to all recipients of the list and ensures that they reach the maintainer of the list, who may not actually read the list.

Depending on the structure of the list, it is relatively easy to copy all of the recipients' e-mail addresses and add them to another list without permission; this is considered an invasion of privacy, though, and should not be done. In fact, that sort of copying is why many Web sites now have a privacy policy that assures users they won't share mailing lists with third parties.