title: CQRS - When to send confirmation message?
body: <blockquote>
    <p><strong>Example:</strong> Business rules states that the customer should get a confirmation message (email or similar) when an order has been placed.</p>
  </blockquote>
  
  <p>Lets say that a <code>NewOrderRegisteredEvent</code> is dispatched from the domain and is picked up by an event listener that sends of the confirmation message. When that is done some other event handler throws an exception or something else goes wrong and the unit of work is rolled back. We've now sent the user a confirmation message for something that was rolled back. </p>
  
  <p>What is the "cqrs" way of solving problems like this where you want to do something after a unit of work has been committed? Another complicating factor is replaying of events. I don't want old confirmation messages to be re-sent whenever I replay recorded events in order to build a new view / projection. </p>
  
  <p><em>My best theory so far: I've just started to look into the fascinating world of cqrs and was wondering whether this is something that would be implemented as a saga? If a saga is like a state machine where each transition only can take place a single time then I guess that would solve this problem? I just have a hard time visualizing how this will fit together with the command bus and domain events..</em> </p>