Would it be possible to create a plugin for users to subscribe to an individual seller's news letter? So that the seller could email them when any promotion is going on. How it would work is that when a user see a seller he wants to receive updates from he would subscribe to their news letter. The seller intern wouldn't be able to see the email addresses of who is subscribe to them, all that should be visible is the total number of subscribers and their names. Also a link would be created in the user's account for example saying "Manage Subscription" when clicked the user can see who he is subscribe to and can unsubscribe if needs be.