function check_form()
{
  f = document.unsubscribe;
  err = new Error();
  if (isempty(f.email) || f.email.value == "your email") err.add('Email is mandatory. Please re-enter.');
  
  if (err.isset()){
    err.show();
    return false;
  }
  f.submit();
  return true;
}