Validacion de Email y dominios

Valida las entradas de email y dominos
codigo de Shantanu's Blog

<?php

function validate_email($email){

$exp = "^[a-z\'0-9]+([._-][a-z\'0-9]+)*@([a-z0-9]+([._-][a-z0-9]+))+$";

if(eregi($exp,$email)){
 if(checkdnsrr(array_pop(explode("@",$email)),"MX")){
  print("$email is ok.
");
   }else{
   print("$email is ok. But domain is not.
");
   }
    }else{
    print("$email is not ok.
");
    } 
}

validate_email("shantanu.ok");
validate_email("shantanu.ok@gmail.com");
validate_email("shantanu.ok@fsjaldkfjlsfjsljflsfjsldk.com");

?>