title: When publishing message with mqtt QoS 2, can it be lost?
body: <p>I am trying to implement an MQTT client, using <a href="https://github.com/novastone-media/MQTT-Client-Framework/tree/master/MQTTClient" rel="noreferrer">MQTT-Client Framework</a>. I want to assure that every message I try to publish reaches the broker. I can't figure out exactly what QOS2 means: It states that a message will be sent exactly once. Does it mean that when connection is lost, it will try to retransmit the message automatically after reconnecting? Or this should be handled by the app?  </p>
  
  <p>Also in this library, reconnection is done by default automatically? Or there is need to check if connectionLost happens and then try to reconnect?</p>