No matter how hard you try my friend, users will still be able to enter incorrect email addresses.
One way is to do what we do here at Stardeveloper. Receive the email address and after syntax checking, create a unique number and save it in the database, send an email to the email address specified along with unique number asking the user to enter this number in a form on the site, if the user's email was correct he/she'll receive the email and correctly enter the number in the form on the site, the form on the site will then remove the unique number from the database and allow the user to proceed.