On the major computer networks, there are many discussion groups that use electronic mail to send articles to the people in the group. The groups are sometimes known on the Internet as SIGs (Special Interest Groups) and often known on BITNET as listservs; they are most commonly called mailing lists.
An ad hoc group can be formed simply by including a group of addresses in any mail message, and if everyone uses reply all (or the equivalent), a discussion can continue.
A network mailing list is maintained at some central site, where someone takes care of maintaining the list of addresses. Normally, the members of the list contribute an article by mailing it to a special address at the central site, and a program remails it to everyone on the list. Someone who acts as the list maintainer has two main duties: take requests for people who want to subscribe or unsubscribe to the list, and follow up mail returned as nondeliverable (often meaning someone's account expired).
Lists of lists are maintained on most hosts. There is no single registry for such lists, so there are a few different major lists of lists and also many specialized lists of lists with narrower scope of subject matter. Lists may be announced or listed in articles sent to people on other lists, and people sometimes post a query to one list asking if anyone knows of a list on a related topic.
For Internet lists, usually there are two special addresses, listname@host and listname-request@host. Use the -request address to talk to the list maintainer, mainly to subscribe or unsubscribe, and use the regular listname@host address only to send articles.
Suppose there is a list called gnomes maintained at foobar.baz.edu, and it has a gnomes-request address. You would subscribe or unsubscribe to the list by sending a message to the -request address.
MM>send To: gnomes-request@foobar.baz.edu cc: Subject: Message (End with CTRL/D or ESC Use CTRL/B to insert a file, CTRL/E to enter editor, CTRL/F to run text through a filter, CTRL/K to redisplay message, CTRL/L to clear screen and redisplay, CTRL/N to abort, CTRL/P to run a program and insert output.): Please put me on the gnomes mailing list. Thanks, Fred Flange.
To post an article for people to read, send it to the list name, gnomes@foobar.baz.edu.
Some lists do not have a -requests address. The announcement or listing about the list should explain how to subscribe. If you don't have good information, try sending to a -requests address first.
To subscribe to a typical BITNET list, you have to send a message to a listserv program. The subscription message is in the format sub listname yourname, and yourname refers to your real name, not computer user name. Listserv gets your address from the From field of the message. To unsubscribe, send the message unsub listname.
If the gnomes list were maintained by a listserv at the BITNET node foobar, the subscribe message would look like this. Be sure to notice that the subscribe message is addressed to the listserv and not to the name of the list.
MM>send To: listserv@foobar.bitnet cc: Subject: Message (End with CTRL/D or ESC Use CTRL/B to insert a file, CTRL/E to enter editor, CTRL/F to run text through a filter, CTRL/K to redisplay message, CTRL/L to clear screen and redisplay, CTRL/N to abort, CTRL/P to run a program and insert output.): sub gnomes Fred Flange
To post an article for people to read, send it to the list address, gnomes@foobar.bitnet.
After you subscribe, you should get one or two messages from the list maintainer with more information. Keep the message. It should include the personal address of the list maintainer, who you can contact if you run into any problem with mail to or from the list. It should also say explicitly how to get off the list.
If you go on vacation, consider unsubscribing to any voluminous lists, so your mailbox will not fill up while you're away. You can easily re-subscribe. It is also polite to unsubscribe to lists when your computer account is about to expire, to save the list maintainer the trouble of getting mail returned from your expired address.
Although it is a different system than electronic mail, the Usenet Netnews should be mentioned here, since its purpose, electronic discussion groups, is essentially the same as the mailing lists described above. The main advantage of Netnews over mail is that the articles (messages) are stored centrally, so they don't use up your own disk space and aren't intermingled with your other mail. The disadvantage is that you might be on a host that supports mail but doesn't carry Usenet. Some mailing lists are gatewayed with Usenet newsgroups, so the same forum is available by either method. You don't read or send Usenet articles with MM, but with some other program, perhaps rn, trn or tin.