While Notes always had the option for custom mail experiences (store form in document, send), the Embedded Experiences allow integration into any application (that supports them).
One of the first things you might want to do is to pimp your existing applications to provide this new experience. It would be much lighter than storing the form and also work with other mail front-ends.
The good news: adding embedded experiences degrades gracefully, so all users not on 9.0 or later won't see a thing. This means you can get started immediately:
- listen to Niklas' explanation and get the sample code
- create/configure the gadget for your application (that's a separate post, coming soon), check the documentation
- create a class that does all the notification sending, classic and EE
As ususal YMMV