Using MX records to validate email addresses

Question

Scenario:
I have a contact form on my web app, it gets alot of spam.
I am validating the format of email addresses loosely i.e. ^.+@.+\\..+$

Answer 1

function mxrecordValidate($email){
        list($user, $domain) = explode('@', $email);
        $arr= dns_get_record($domain,DNS_MX);
        if($arr[0]['host']==$domain&&!empty($arr[0]['target'])){
                return $arr[0]['target'];
        }
}
$email= 'user@radiffmail.com';

if(mxrecordValidate($email)) {
        echo('This MX records exists; I will accept this email as valid.');
}
else {
        echo('No MX record exists;  Invalid email.');
}