<?
if( validate_email($email) == true ){
   echo "Yay! $email is valid!";
}else{
   echo "Sorry, $email is not a valid email address.";
}
?>

<?php

function validate_email($email){
   if (eregi("(@.*@)|(\.\.)|(@\.)|(\.@)|(^\.)", $email) ||
      !eregi ("^.+\@(\[?)[-_a-zA-Z0-9\.]+\.([a-zA-Z]{2,3}|[0-9]{1,3})(\]?)$", $email)) {
      return(false);
   } else {
      list($user, $domain) = explode("@", $email);
      if ((!eregi("^[_a-zA-Z0-9\.\-]+$", $user)) ||
         (!eregi("^[_a-zA-Z0-9\.\-]+$", $domain))) {
         return false;
      } else {
         return(true);
      }
   }
}

?>