Can this plugin be used independently on each sub site?

Can this plugin be used independently on each sub site?

If not, any other solution may do that?

I want sub site admin to send emails to his sub website's subsribers, not to all the users on the WPMU network.

Another question, when people sign up on his sub site, how to automatically assign new users as his sub site's subscriber in a WP MU network setup inviroment?

Thanks :slight_smile: