Mailing Lists enable users to subcribe to notifications from your website, such as Newsletters. This video shows it in use on a website.
This Help Resource demonstrates how a website visitor user registers interest / joins a Mailing List. The Mailing List Manager Atom has been added to a web page and configured to add Users to a selected Mailing List.
In the event that the visitor doesn't yet have an account, the Atom will enable them to create a new User account, as a child of a selected Group.
In the accompanying video we can see a User attempt to join a Mailing List without having logged in. They then try to create a new Account, using their email address. The system recognises that the email address is already in use and so does not create the account, providing a message to advise them to log in. They then log in with their old account and subscribe to the selected Mailing List.