diff --git a/Source/MQTTnet/Client/Publishing/MqttClientPublishResult.cs b/Source/MQTTnet/Client/Publishing/MqttClientPublishResult.cs
index d58ad581..a523fe55 100644
--- a/Source/MQTTnet/Client/Publishing/MqttClientPublishResult.cs
+++ b/Source/MQTTnet/Client/Publishing/MqttClientPublishResult.cs
@@ -8,7 +8,7 @@ namespace MQTTnet.Client.Publishing
         /// <summary>
         /// Gets the packet identifier which was used for this publish.
         /// </summary>
-        public ushort PacketIdentifier { get; set; }
+        public ushort? PacketIdentifier { get; set; }
 
         /// <summary>
         /// Gets or sets the reason code.
diff --git a/Source/MQTTnet/Server/Internal/MqttClientSession.cs b/Source/MQTTnet/Server/Internal/MqttClientSession.cs
index c0894a24..3aa8db5a 100644
--- a/Source/MQTTnet/Server/Internal/MqttClientSession.cs
+++ b/Source/MQTTnet/Server/Internal/MqttClientSession.cs
@@ -14,7 +14,7 @@ namespace MQTTnet.Server.Internal
     {
         readonly MqttPacketBus _packetBus = new MqttPacketBus();
 
-        readonly Dictionary<ushort, MqttPublishPacket> _publishPacketsWithoutAcknowledge = new Dictionary<ushort, MqttPublishPacket>();
+        readonly Dictionary<ushort, MqttPublishPacket> _unacknowledgedPublishPackets = new Dictionary<ushort, MqttPublishPacket>();
 
         readonly IMqttServerOptions _serverOptions;
         readonly MqttClientSessionsManager _clientSessionsManager;
@@ -56,7 +56,7 @@ namespace MQTTnet.Server.Internal
 
         public void AcknowledgePublishPacket(ushort packetIdentifier)
         {
-            _publishPacketsWithoutAcknowledge.Remove(packetIdentifier);
+            _unacknowledgedPublishPackets.Remove(packetIdentifier);
         }
         
         public void EnqueuePacket(MqttPacketBusItem packetBusItem)
@@ -80,7 +80,7 @@ namespace MQTTnet.Server.Internal
             {
                 if (publishPacket.QualityOfServiceLevel > MqttQualityOfServiceLevel.AtMostOnce)
                 {
-                    _publishPacketsWithoutAcknowledge[publishPacket.PacketIdentifier] = publishPacket;
+                    _unacknowledgedPublishPackets[publishPacket.PacketIdentifier] = publishPacket;
                 }
                 
                 _packetBus.Enqueue(packetBusItem, MqttPacketBusPartition.Data);
@@ -116,7 +116,7 @@ namespace MQTTnet.Server.Internal
             // TODO: Check if packet identifier must be restarted or not.
             _packetBus.Clear();
 
-            foreach (var publishPacket in _publishPacketsWithoutAcknowledge.Values.ToList())
+            foreach (var publishPacket in _unacknowledgedPublishPackets.Values.ToList())
             {
                 EnqueuePacket(new MqttPacketBusItem(publishPacket));
             }
diff --git a/Tests/MQTTnet.Core.Tests/Client/MqttClient_Tests.cs b/Tests/MQTTnet.Core.Tests/Client/MqttClient_Tests.cs
index 5e96c0cd..3e9d8923 100644
--- a/Tests/MQTTnet.Core.Tests/Client/MqttClient_Tests.cs
+++ b/Tests/MQTTnet.Core.Tests/Client/MqttClient_Tests.cs
@@ -684,51 +684,7 @@ namespace MQTTnet.Tests.Client
                 Assert.AreEqual("DA|18RS00SC00XI0000RV00R100R200R300R400L100L200L300L400Y100Y200AC0102031800BELK0000BM0000|", receivedMessages.First().ConvertPayloadToString());
             }
         }
-
-        [TestMethod]
-        public async Task Message_Send_Retry()
-        {
-            using (var testEnvironment = CreateTestEnvironment())
-            {
-                testEnvironment.IgnoreClientLogErrors = true;
-                testEnvironment.IgnoreServerLogErrors = true;
-
-                await testEnvironment.StartServer(
-                    new MqttServerOptionsBuilder()
-                        .WithPersistentSessions()
-                        .WithDefaultCommunicationTimeout(TimeSpan.FromMilliseconds(250)));
-
-                var client1 = await testEnvironment.ConnectClient(new MqttClientOptionsBuilder().WithCleanSession(false));
-                await client1.SubscribeAsync("x", MqttQualityOfServiceLevel.AtLeastOnce);
-
-                var retries = 0;
-
-                async Task Handler1(MqttApplicationMessageReceivedEventArgs eventArgs)
-                {
-                    retries++;
-
-                    await Task.Delay(1000);
-                    throw new Exception("Broken!");
-                }
-
-                client1.UseApplicationMessageReceivedHandler(Handler1);
-
-                var client2 = await testEnvironment.ConnectClient();
-                await client2.PublishAsync("x");
-
-                await Task.Delay(3000);
-
-                // The server should disconnect clients which are not responding.
-                Assert.IsFalse(client1.IsConnected);
-
-                await client1.ReconnectAsync().ConfigureAwait(false);
-
-                await Task.Delay(1000);
-
-                Assert.AreEqual(2, retries);
-            }
-        }
-
+        
         [TestMethod]
         public async Task NoConnectedHandler_Connect_DoesNotThrowException()
         {