Email notification to admin users for registration form

Hi,
I'm using Sitefinity 6.1.
First of all, I know that for normal forms (Contents > Forms), a backend user can subscribe to get email notifications after someone submit it. (Correct me if I'm wrong).
But for registration form, which is put in the page via Registration widget, not Form widget, how can I setup the email notification for admin users? I've already tried creating a C# class inherits RegistrationForm and override SendRegistrationConfirmationEmail function. Then set RegistrationFormTypeName to MyNameSpace.MyClass. But I don't know why I cannot save it (save then open again and see the old class).

Lastly, if I use code, the admin email will be fixed. How can I make it configurable?

Thanks for reading,
Harry

Hello,

 Thank you for the detailed information provided.

Yes, you are right that every time a Sitefinity user is created or a user completes the form (created under Content -> Form), he or she is also added as a subscriber to the mailing list. Could you please send me your code so that I can inspect it and be able to help you.

Thank you!