A listserv is a discussion of a particular topic, which may have a mediator. Listservs are conducted entirely through email, although they may be archived in other parts of the Internet. These listservs have a high volume of interaction, which will fill up your email-box. You may want to try them one at a time. Also, when you subscribe you will receive a message that confirms your subscription; it also contains the information that will tell you how to unsubscribe.