The web interface offers both methods. When using a password, it is able
to tell you whether you are on the list or not and to allow you to change
your subscription options or e-mail address on the fly. Everything
happens synchronously and without surprise. When using the screen that
does not require a password, the interface cannot even tell you if the
address you typed is subscribed, and there is no way to change your
subscription options (because they cannot be queried). You just get a box
in which you can type an e-mail address, then you click on "Join" or
"Leave" and it sends you e-mail.
Eric