title: Magento Newletter subscription - show error if already subscribed
body: <p>Hi I am using default newsletters subscription package in magento. I need to show an error if the user is already registered with Us I've seen an option like this</p>
  
  <pre><code>    $emailExist = Mage::getModel('newsletter/subscriber')-&gt;load($email, 'subscriber_email');
      if ($emailExist-&gt;getId()) {
        Mage::throwException($this-&gt;__('This email address is already exist.'));
      }
  </code></pre>
  
  <p>from here <a href="https://stackoverflow.com/questions/17289289/show-error-message-in-guest-subscriber-if-user-already-subscribe-with-that-id/19755281#19755281">Show error message in guest subscriber if user already subscribe with that Id</a> </p>
  
  <p>But this is not working for me, still i am getting same thanks for subscription message. thanks</p>