A list server is software that automatically handles people being added to and people being deleted from your e-mail list. Using the list server, the customer controls whether or not they receive the e-mail. The visitor sees your offer to join the list. If they want to get on the list, they subscribe by giving their e-mail address. If they subscribe and later find out they don't want to receive the e-mail any more, they simply take themselves off the list by unsubscribing.
List servers are a wonderful marketing tool.
So wonderful, you should try one. The closest one to try is on this page. A self-generated subscriber list is the ultimate marketing tool as long as you don't abuse it. There are other marketing tools for getting the initial permission like opt-in mailing lists. Opt-in lists can be good.