title: Redirect to referrer URL but add something to the querystring
body: <p>Using ASP.Net MVC, I'm posting off to an action (where I'm then adding an email address to a DB table etc.)</p>
  
  <p>I need to re-direct back to the referrer URL but also need to add something to the querystring of the referrer URL. This action can be called from many places, so I can't redirect to an action in the current controller.</p>
  
  <p>How do I re-direct to the referrer and add something to the query string (bearing in mind that the referrer might already have query string values that I'll need to preserve).</p>
  
  <pre><code>[HttpPost]
  public ActionResult MyAction(MyModel model)
  {
      //Do stuff.
  
      return new RedirectResult(Request.UrlReferrer.ToString()); // + query string value?
  }
  </code></pre>
  
  <p>Thanks!</p>