Email validity check

PHP code:

<pre lang="php">
<?php 
function is_email($email) {
  $x = '\d\w!\#\$%&\'*+\-/=?\^_`{|}~';    //just for clarity
  return   count($email = explode('@', $email, 3)) == 2 && 
      strlen($email[0]) < 65 && strlen($email[1]) < 256 && 
      preg_match("#^[$x]+(\.?([$x]+\.)*[$x]+)?$#", $email[0]) && 
      preg_match('#^(([a-z0-9]+-*)?[a-z0-9]+\.)+[a-z]{2,6}.?$#', $email[1]);
}
?>
</pre>