diff --git a/hbmqtt/mqtt/protocol/handler.py b/hbmqtt/mqtt/protocol/handler.py
index 4390481..8530759 100644
--- a/hbmqtt/mqtt/protocol/handler.py
+++ b/hbmqtt/mqtt/protocol/handler.py
@@ -168,7 +168,7 @@ class ProtocolHandler:
         :return:
         """
         assert app_message.qos == QOS_1
-        if app_message.is_acknowledged():
+        if app_message.puback_packet:
             raise HBMQTTException("Message '%d' has already been acknowledged" % app_message.packet_id)
         if isinstance(app_message, OutgoingApplicationMessage):
             if app_message.packet_id not in self.session.inflight_out:
@@ -190,11 +190,14 @@ class ProtocolHandler:
             yield from waiter
             del self._puback_waiters[app_message.packet_id]
             app_message.puback_packet = waiter.result()
+
+            # Discard inflight message
+            del self.session.inflight_out[app_message.packet_id]
         elif isinstance(app_message, IncomingApplicationMessage):
             # Initiate delivery
             yield from self.session.delivered_message_queue.put(app_message)
             # Send PUBACK
-            puback = app_message.build_puback_packet()
+            puback = PubackPacket.build(self.packet_id)
             yield from self._send_packet(puback)
             app_message.puback_packet = puback
 
@@ -210,56 +213,70 @@ class ProtocolHandler:
         """
         assert app_message.qos == QOS_2
         if isinstance(app_message, OutgoingApplicationMessage):
-            # Store message
-            publish_packet = None
-            if app_message.publish_packet is not None:
-                # This is a retry flow, no need to store just check the message exists in session
-                if app_message.packet_id not in self.session.inflight_out:
-                    raise HBMQTTException("Unknown inflight message '%d' in session" % app_message.packet_id)
-                publish_packet = app_message.build_publish_packet()
-            else:
-                # Store message in session
-                self.session.inflight_out[app_message.packet_id] = app_message
-                publish_packet = app_message.build_publish_packet()
-
-            # Send PUBLISH packet
-            yield from self._send_packet(publish_packet)
-            app_message.publish_packet = publish_packet
-
-            if not app_message.pubrec_packet:
+            if app_message.pubrel_packet and app_message.pubcomp_packet:
+                raise HBMQTTException("Message '%d' has already been acknowledged" % app_message.packet_id)
+            if not app_message.pubrel_packet:
+                # Store message
+                publish_packet = None
+                if app_message.publish_packet is not None:
+                    # This is a retry flow, no need to store just check the message exists in session
+                    if app_message.packet_id not in self.session.inflight_out:
+                        raise HBMQTTException("Unknown inflight message '%d' in session" % app_message.packet_id)
+                    publish_packet = app_message.build_publish_packet(dup=True)
+                else:
+                    # Store message in session
+                    self.session.inflight_out[app_message.packet_id] = app_message
+                    publish_packet = app_message.build_publish_packet()
+                # Send PUBLISH packet
+                yield from self._send_packet(publish_packet)
+                app_message.publish_packet = publish_packet
+                # Wait PUBREC
                 if app_message.packet_id in self._pubrec_waiters:
                     # PUBREC waiter already exists for this packet ID
                     message = "Can't add PUBREC waiter, a waiter already exists for message Id '%s'" \
                               % app_message.packet_id
                     self.logger.warning(message)
                     raise HBMQTTException(message)
-                # Wait for PUBREC
                 waiter = asyncio.Future(loop=self._loop)
                 self._pubrec_waiters[app_message.packet_id] = waiter
                 yield from waiter
                 del self._pubrec_waiters[app_message.packet_id]
                 app_message.pubrec_packet = waiter.result()
-
-            if not app_message.pubrel_packet:
+            if not app_message.pubcomp_packet:
                 # Send pubrel
                 app_message.pubrel_packet = PubrelPacket.build(app_message.packet_id)
                 yield from self._send_packet(app_message.pubrel_packet)
-
-            if not app_message.pubcomp_packet:
                 # Wait for PUBCOMP
                 waiter = asyncio.Future(loop=self._loop)
                 self._pubcomp_waiters[app_message.packet_id] = waiter
                 yield from waiter
                 del self._pubcomp_waiters[app_message.packet_id]
                 app_message.pubcomp_packet = waiter.result()
-
+            # Discard inflight message
+            del self.session.inflight_out[app_message.packet_id]
         elif isinstance(app_message, IncomingApplicationMessage):
-            if app_message.publish_packet.dup_flag:
-                self.logger.warning("[MQTT-3.3.1-2] DUP flag must set to 0 for QOS 0 message. Message ignored: %s" %
-                                    repr(app_message.publish_packet))
-            else:
-                # Assign packet_id as it's needed internally
-                yield from self.session.delivered_message_queue.put(app_message)
+            self.session.inflight_in[app_message.packet_id] = app_message
+            # Send pubrec
+            pubrec_packet = PubrecPacket.build(app_message.packet_id)
+            yield from self._send_packet(pubrec_packet)
+            app_message.pubrec_packet = pubrec_packet
+            # Wait PUBREL
+            if app_message.packet_id in self._pubrel_waiters:
+                # PUBREL waiter already exists for this packet ID
+                message = "Can't add PUBREC waiter, a waiter already exists for message Id '%s'" \
+                          % app_message.packet_id
+                self.logger.warning(message)
+                raise HBMQTTException(message)
+            waiter = asyncio.Future(loop=self._loop)
+            self._pubrel_waiters[app_message.packet_id] = waiter
+            yield from waiter
+            del self._pubrel_waiters[app_message.packet_id]
+            app_message.pubrel_packet = waiter.result()
+            #Discard message
+            del self.session.inflight_in[app_message.packet_id]
+            # Send pubcomp
+            pubcomp_packet = PubcompPacket.build(app_message.packet_id)
+            yield from self._send_packet(pubcomp_packet)
 
     @asyncio.coroutine
     def stop(self):