Email validity check

PHP code:

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]);
}