Anonymous user can't unsubscribe

Currently there is no way for an anonymous user to unsubscribe from the mailing list. If I go to the url, for example: www.example.com/mlm/ where the email address that I want to unsubscribe is the last part of the url, then I get a page that has a checkbox showing that I am subscribed to the list. If I uncheck the box and hit "Save Preferences," the screen comes back the way it was before, with the box still checked. Only if I'm logged in as a site administrator can I unsubscribe a user.

In addition, there should be an unsubscribe link added to the send body of the email once the above is working. To do this, the module should have access to the %to parameter so that the recipient's email address can be in the link.