Made deliveryCount a local variable.

Source/MQTTnet/MqttApplicationMessage.cs

@@ -29,7 +29,5 @@ namespace MQTTnet
         public byte[] CorrelationData { get; set; }
 
         public List<uint> SubscriptionIdentifiers { get; set; }
-
-        internal uint DeliveryCount { get; set; }
     }
 }

Source/MQTTnet/Server/MqttClientSession.cs

@@ -56,8 +56,6 @@ namespace MQTTnet.Server
 
             _logger.Verbose("Queued application message with topic '{0}' (ClientId: {1}).", applicationMessage.Topic, ClientId);
 
-            applicationMessage.DeliveryCount++;
-
             ApplicationMessagesQueue.Enqueue(applicationMessage, senderClientId, checkSubscriptionsResult.QualityOfServiceLevel, isRetainedApplicationMessage);
         }
 

Source/MQTTnet/Server/MqttClientSessionsManager.cs

@@ -224,7 +224,7 @@ namespace MQTTnet.Server
                     await _retainedMessagesManager.HandleMessageAsync(sender?.ClientId, applicationMessage).ConfigureAwait(false);
                 }
 
-                applicationMessage.DeliveryCount = 0;
+                var deliveryCount = 0;
 
                 foreach (var clientSession in _sessions.Values)
                 {
@@ -232,9 +232,11 @@ namespace MQTTnet.Server
                         applicationMessage,
                         sender?.ClientId,
                         false);
+
+                    deliveryCount++;
                 }
 
-                if (applicationMessage.DeliveryCount == 0)
+                if (deliveryCount == 0)
                 {
                     if (_options.UndeliveredMessageInterceptor == null)
                     {