function check_email_address($email) {
  if (!ereg("^[^@]{1,64}@[^@]{1,255}$", $email)) {
    return false;
  }

  $email_array = explode("@", $email);
  $local_array = explode(".", $email_array[0]);
  for ($i = 0; $i < sizeof($local_array); $i++) {
    if (!ereg("^(([A-Za-z0-9!#$%&'*+/=?^_`{|}~-][A-Za-z0-9!#$%&�'*+/=?^_`{|}~\.-]{0,63})|(\"[^(\\|\")]{0,62}\"))$",$local_array[$i])) {
      return false;
    }
  }

  if (!ereg("^\[?[0-9\.]+\]?$", $email_array[1])) {
    $domain_array = explode(".", $email_array[1]);

    if (sizeof($domain_array) < 2) {
      return false;
    }
    for ($i = 0; $i < sizeof($domain_array); $i++) {
      if (!ereg("^(([A-Za-z0-9][A-Za-z0-9-]{0,61}[A-Za-z0-9])|�([A-Za-z0-9]+))$",$domain_array[$i])) {
        return false;
      }
    }
  }
  return true;
}

Email validation

PHP