We are using WPMU for our wedding site builder and need a RSVP plugin that works 100%

Please can you provide a solution? We have developed a wedding site builder that needs an effective rsvp plugin that automatically send out wedding invitations and that notifies the customer that has built a site on our multisite to get emails notifying them that guests have RSVP'd. The plugin that i am using works but send out the wedding invitation through the plugin from our admin email and does not notify when someone replies/rsvp
Do you have a solution plugin that has a default wedding invitation and that will notify the person that actually owns the wedding site?

Thanks