Mailing lists are a powerful feature. They allow you to send mail to many correspondents with a single command. They may be used internally (for example, to send mail to the whole sales department) or externally (for example, to send mail to all registered users of one of your products).

Mailing lists have many uses and configurations. You can set up a list with only the members that you choose on it, or you can set up a list anyone can join by sending a subscription request to your mail server. You can set the list up so that it functions as a discussion group in which any member can send mail to all the other members, or you can set it up more like a broadcast medium so that only you can send messages.