Just make it easy for everyone to create their own mailing list. Then you could subscribe to friends, and get updates from them, plus participate in discussion

Just make it easy for everyone to create their own mailing list. Then you could subscribe to friends, and get updates from them, plus participate in discussions with their other friends. "Muting" a friend would be up to the controls in your desired email client. "Unfriending" is simply unsubscribing.