Listserv is an automated email mailing list, maintained entirely by a computer. Listserv is only one type of automated service, Majordomo is another. Soft Ventures' SVList lets you run a list from your PC using any email account you choose. Most programs have common command features. One can subscribe, unsubscribe, read archived messages, and issue other commands via email.
Some lists have thousands of subscribers and can result in hundreds of email messages a day.
I subscribe to Net-Happenings which give me 4 to 5 digests per day of newly established web sites. There are a number of listservs of interest to those in criminology. I have a links page to some of them. The best is maintained by Diane K. Kovacs and includes lists related to forensic science, police, law, etc. Push publishing technologies permit the user to subscribe to a number of Internet resources at once and then to receive updates automatically or at the user's convenience.