Like the other comments noted, you won't go far with email verification alone (they might even use a completely unrelated email address). You can probably use a

Like the other comments noted, you won't go far with email verification alone (they might even use a completely unrelated email address). You can probably use a combination of email address similarity and ip address uniqueness but I think mobile verification would be much more reliable(and thanks to cheap sms via twilio, won't break your bank)