Mailing lists are centrally managed, and have a "reflector" or central distribution point (what you call a "robot") which maintains the email addresses of all the people on the mailing list. In order to add or remove yourself to the mailing list, you typically have to send a message to name-of-mailing-list-REQUEST, not to the whole mailing list of course. Now days there are usually web pages that people can use to subscribe and unsubscribe and view the archives, and which the administrator can use to moderate messages, but in the old days the moderator was a human and administered the list via email. To save bandwidth (in the days that it mattered, i.e. over the slow ARPANET and over international connections and expensive dial up modems) there would be redistribution lists for regions and organizations, which users or local administrators would have to manage themselves (or the central administrator would have to forward requests to the redistribution list administrator), so only one copy of the message had to be sent to each redistribution list.
https://en.wikipedia.org/wiki/Electronic_mailing_list
An electronic mailing list or email list is a special use of email that allows for widespread distribution of information to many Internet users. It is similar to a traditional mailing list — a list of names and addresses — as might be kept by an organization for sending publications to its members or customers, but typically refers to four things:
1) a list of email addresses,
2) the people ("subscribers") receiving mail at those addresses,
3) the publications (email messages) sent to those addresses, and
4) a reflector, which is a single email address that, when designated as the recipient of a message, will send a copy of that message to all of the subscribers.
