I answered in your support ticket, but I will copy my answer here, as well:
We already have the "stop from login until confirmation" logic implemented. However, confirmation email is by default sent to the registering user, so you need to change it to be always sent to the admin email, so that the admin can approve the registering user. Here's what you need to do:
1) Inherit from RegistrationForm and change the user's email to be the desired one:
CustomRegistration : RegistrationForm
SendRegistrationConfirmationEmail(Telerik.Sitefinity.Security.Model.User user, Telerik.Sitefinity.Security.UserManager userManager)
2) Now build your project and go to Administration >> Settings >> Advanced >> Toolboxes >> Sections, create a new section (Custom) and register your custom Registration widget by entering Namespace.Class in the type field and then whatever title and name for the widget that you desire.
3) Now place your newly registered widget on a page (no the default registration, but the custom one that you made) and click Edit. Then go to Account Activation and choose the "After confirmation" radio button. Choose a confirmation page and click Save.
Now when your users register, an email would be sent to the email that you specified and only until after the link in this email has been clicked, they will be able to log in. Also, don't forget that you will need SMTP settings in order to send e-mails.
All the best,
the Telerik team
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