Using MX records to validate email addresses

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= '[email protected]';

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

DNS lookups can be slow at times, depending on network traffic & congestion, so that's something to be aware of.

If I were in your shoes, I'd test it out and see how it goes. For a week or so, log all emails to a database or log file and include a field to indicate if it would be marked as spam or legitimate email. After the week is over, take a look at the results and see if it's performing as you would expect.

Taking this logging/testing approach gives you the flexibility to test it out and not worry about loosing customer emails.

I've gotten into the habit of adding an extra field to my forms that is hidden with CSS, if it's filled in I assume it's being submitted by a spam bot. I also make sure to use a name like "url" or "website_url" something that looks like a legitimate field name to a spam bot. Add a label for the field that says something like "Don't fill out this field" so if someone's browser doesn't render it correctly, they will know not to fill out the spam field. So far it's working very well for me.

//The Code *https://davidwalsh.name/php-email-validator*  
function domain_exists($email, $record = 'MX'){
    list($user, $domain) = explode('@', $email);
    return checkdnsrr($domain, $record);
}

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

I see no harm doing a MX lookup with checkdnsrr() and I also don't see how false positives may appear. You don't need to escape the hostname, in fact you can use this technique and take it a little further by talking to the MTA and testing if the user exists at a given host (however this technique may and probably will get you some false positives in some hosts).