Check email in Php

<?php
if(checkemailaddress("nat@natrert.it")){echo "mail valida";}else{echo "no";}
?>
<?php
function checkemailaddress($email) {
  if(preg_match("/^([a-zA-Z0-9])+([a-zA-Z0-9\._-])*@([a-zA-Z0-9_-])+([a-zA-Z0-9\._-]+)+$/",$email)){
    list($username,$domain)=split('@',$email);
    if(!checkdnsrr($domain,'MX')) {
      return false;
    }
    return true;
  }
  return false;
}
?>