As a substitute of a bot, MassMessage inherits a subscription model based on entries listed in wiki pages. This is a very fragile process, open to abuse and user mistakes. It is also a process that puzzles most humans out there.
Imagine a World in which users could subscribe and unsubscribe from MassMessage notifications through their user preferences.
A first step wold be very basic: subscribe to all notifications / unsubscribe from all notifications. A possible next step would be to allow subscriptions per "channels" or "newsletters".