So first, how does the user know what possible discussion groups exist? A file containing a list of some international Internet mailing lists can be obtained by anonymous ftp on ftp.nisc.sri.com in netinfo/interest-groups. There are over 800 lists mentioned in that file from mailing lists on network protocols, to bird watching and the human geome project. However, there are thousands more both international and local, run by organisations, governments, special interest groups or by individuals. In order to join the lists of choice a user simply sends an e-mail message to the appropriate host. For each mailing list there is a designated host SERVER. The general convention for being adder to a mailing list is to sent an empty message to the host at list-request@host. There are several types of mailing list:

1. unmoderated lists allow free discussion. There are no restrictions on the messages sent. These types of list generally have quick response times but high traffic
2. moderated lists are ones where all the messages are read by a "moderator". If the moderator feels a message is appropriate, focuses on the correct subject then he forwards to onto the list. Traffic on a moderated list is less heavy, better quality but often has a slow response time.
3. digest lists are also quite common. For a digest list the moderator collects all the messages together into one big file which is then sent to the list. This type of list is used for topics that receive heavy traffic and reduces the load on the network.