Detect if domain uses Gapps for email

gistfile1.php

<?php
// Determine if this is a Google-hosted account
$isGoogle = false;
if(!empty($_GET['inf_field_Email'])){
	list($name, $domain) = explode('@', urldecode($_GET['inf_field_Email']));
	if($domain == 'gmail.com'){
		$isGoogle = true;
	} elseif(getmxrr($domain, $mxHosts)){
		foreach($mxHosts as $mx){
			if(stripos($mx, 'google') !== false){ $isGoogle = true; }
		}
	}
}