public static function getSmtpFromMx($mx)
 {
     reset(PostmanSmtpMappings::$mxMappings);
     while (list($domain, $smtp) = each(PostmanSmtpMappings::$mxMappings)) {
         if (PostmanUtils::endswith($mx, $domain)) {
             return $smtp;
         }
     }
     return false;
 }