Good evening Phil and welcome back!
Thank you for reaching out to us.
I would love to help you with this topic.
Built-in, there is no option that allows for site owners to get notified whenever an RSVP ticket is used in Event Tickets.
Using Events Tickets Plus will provide such a functionality, but via the e-commerce plugin of your choice (WooCommerce, EDD, etc..), not for RSVP tickets specifically.
In order to get notified whenever somebody purchases an RSVP plugin, you will need to use a plugin such as Better Notifications for WordPress.
Basically you will need to add a rule to get notified every time a tribe_rsvp_attendees post is published 🙂
Let me know how that goes.
Best regards,
Geoff B.