Check box in a form?

HI there, thanks by the support first of all.
I’m currently asking if it is possible to have a kind of no static variable in a form.
For example i want to know if email is valid or not… or mean show or not the email.

Is there a way in order to set some control in the form to check if it is valid ?

Can someone help ?

Thanks in advance

I think I’m gonna follow this approach…