title: How to handle failures when one of the router actors throws an exception
body: <p>Say I have an email sender actor that is responsible for sending out emails.
  I want to limit the # of actors created for sending emails, so I created a router.</p>
  
  <pre><code>class EmailSender extends Actor {
  
      val router = context.actorOf(RoundRobinRouter(4).props(EmailSender.props))
  
      def recieve = {
          case SendEmail(emailTo: String, ..) =&gt;
              router ! SendEmailMessage(emailTo,.. )
          case ...
      }
  }
  </code></pre>
  
  <p>I want to understand 2 things here:</p>
  
  <ol>
  <li>If an email message sending fails by one of the router actors, how will EmailSender get notified and will I get the exact email that failed?</li>
  </ol>