Email Verification

Also how do my form check if the email address is authentic or registered. (I'm not talking about email validation that I already know)

Hi, 

As per confirming an email address, you can do this by having an introduction form - form A

Form A can gather simple information such as name and e-mail.

It generates an autoresponder notificaion (e-mail sent to the address entered) 

The autoresponder can have a link to the second form - Form B

You can prepopulate the fields (on Form B) that were already filled out in Form A.

The users filling out your form would only be able to find the second, main form, if they have received the link to it in their email.