Confirmation of registered email address when completing registration form

Customer-controlled web UA (IE, Chrome, Firefox, etc.) and
It's difficult to implement just by web server (such as Apache httpd or IIS).

Usually, middleware (software that dynamically generates HTML) is installed on the web server side. The middleware accesses the database and
·Dynamic generation of HTML for registered email addresses
·Dynamic generation of HTML with unregistered email address
I think you'll end up doing it.Your web UA just displays the HTML.

I would appreciate it if you could ask me another question about what to use as middleware.