That's a nightmare for a user or even the sass provider itself. User has to link every service he signs up for to this sass service. The sass provider must know

That's a nightmare for a user or even the sass provider itself. User has to link every service he signs up for to this sass service. The sass provider must know every type of notification of every software on earth. Or, you're thinking of notification settings on iOS and Android(You can also select which type of notification channels u want to mute). or notification settings on the individual sites.