diff --git a/dotnet/src/ZB.MOM.NatsNet.Server/ClientConnection.SubscriptionsAndDelivery.cs b/dotnet/src/ZB.MOM.NatsNet.Server/ClientConnection.SubscriptionsAndDelivery.cs
new file mode 100644
index 0000000..927c304
--- /dev/null
+++ b/dotnet/src/ZB.MOM.NatsNet.Server/ClientConnection.SubscriptionsAndDelivery.cs
@@ -0,0 +1,482 @@
+// Copyright 2012-2026 The NATS Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+
+using System.Text;
+using ZB.MOM.NatsNet.Server.Internal;
+using ZB.MOM.NatsNet.Server.Internal.DataStructures;
+
+namespace ZB.MOM.NatsNet.Server;
+
+public sealed partial class ClientConnection
+{
+    private const string MqttPrefix = "$MQTT.";
+    private const string ReplyPrefix = "_R_.";
+    private const int MsgScratchSize = 1024;
+    private const int MaxDenyPermCacheSize = 256;
+    private const int MaxPermCacheSize = 128;
+    private const int PruneSize = 32;
+    private static readonly TimeSpan StallMin = TimeSpan.FromMilliseconds(2);
+    private static readonly TimeSpan StallMax = TimeSpan.FromMilliseconds(5);
+    private static readonly TimeSpan StallTotal = TimeSpan.FromMilliseconds(10);
+
+    internal Exception? AddShadowSubscriptions(INatsAccount? acc, Subscription sub)
+    {
+        if (acc is null)
+            return new InvalidOperationException("missing account");
+        _ = sub;
+        return null;
+    }
+
+    internal (Subscription? shadow, Exception? err) AddShadowSub(Subscription sub, object? ime)
+    {
+        _ = ime;
+        var copy = new Subscription
+        {
+            Subject = sub.Subject.ToArray(),
+            Queue = sub.Queue?.ToArray(),
+            Sid = sub.Sid?.ToArray(),
+            Qw = sub.Qw,
+            Client = sub.Client,
+        };
+        return (copy, null);
+    }
+
+    internal bool CanSubscribe(string subject, string? queue = null)
+    {
+        if (Perms is null)
+            return true;
+
+        var checkAllow = !((IsMqtt() || Kind != ClientKind.Client) && subject.StartsWith(MqttPrefix, StringComparison.Ordinal));
+        var allowed = true;
+
+        if (checkAllow && Perms.Sub.Allow is not null)
+        {
+            var result = Perms.Sub.Allow.Match(subject);
+            allowed = result.PSubs.Count > 0;
+            if (!string.IsNullOrEmpty(queue) && result.QSubs.Count > 0)
+                allowed = QueueMatches(queue, result.QSubs);
+
+            if (!allowed && Kind == ClientKind.Leaf && SubscriptionIndex.SubjectHasWildcard(subject))
+            {
+                var reverse = Perms.Sub.Allow.ReverseMatch(subject);
+                allowed = reverse.PSubs.Count != 0;
+            }
+        }
+
+        if (allowed && Perms.Sub.Deny is not null)
+        {
+            var result = Perms.Sub.Deny.Match(subject);
+            allowed = result.PSubs.Count == 0;
+            if (!string.IsNullOrEmpty(queue) && result.QSubs.Count > 0)
+                allowed = !QueueMatches(queue, result.QSubs);
+
+            if (allowed && MPerms is null && SubscriptionIndex.SubjectHasWildcard(subject) && DArray is not null)
+            {
+                foreach (var deny in DArray.Keys)
+                {
+                    if (SubscriptionIndex.SubjectIsSubsetMatch(deny, subject))
+                    {
+                        LoadMsgDenyFilter();
+                        break;
+                    }
+                }
+            }
+        }
+
+        return allowed;
+    }
+
+    internal static bool QueueMatches(string queue, IReadOnlyList<List<Subscription>> qsubs)
+    {
+        if (qsubs.Count == 0)
+            return true;
+
+        foreach (var qsub in qsubs)
+        {
+            if (qsub.Count == 0 || qsub[0].Queue is not { Length: > 0 } q)
+                continue;
+
+            var qname = Encoding.ASCII.GetString(q);
+            if (queue == qname)
+                return true;
+            if (SubscriptionIndex.SubjectHasWildcard(qname) && SubscriptionIndex.SubjectIsSubsetMatch(queue, qname))
+                return true;
+        }
+        return false;
+    }
+
+    internal void Unsubscribe(INatsAccount? acc, Subscription sub, bool force, bool remove)
+    {
+        if (!force && sub.IsClosed())
+            return;
+
+        lock (_mu)
+        {
+            if (remove && sub.Sid is { Length: > 0 } sid)
+                Subs.Remove(Encoding.ASCII.GetString(sid));
+            sub.Close();
+        }
+
+        _ = acc;
+    }
+
+    internal Exception? ProcessUnsub(byte[] arg)
+    {
+        var args = SplitArg(arg);
+        if (args.Count is < 1 or > 2)
+            return new FormatException($"processUnsub Parse Error: {Encoding.ASCII.GetString(arg)}");
+
+        var sid = Encoding.ASCII.GetString(args[0]);
+        lock (_mu)
+        {
+            _in.Subs++;
+            if (!Subs.TryGetValue(sid, out var sub))
+                return null;
+
+            // Max-delivery based deferred unsub is not modeled yet, so unsubscribe immediately.
+            Unsubscribe(Account, sub, force: true, remove: true);
+        }
+
+        if (Opts.Verbose)
+            SendOK();
+
+        return null;
+    }
+
+    internal bool CheckDenySub(string subject)
+    {
+        if (MPerms is null || MPerms.Deny is null)
+            return false;
+
+        if (MPerms.DCache.TryGetValue(subject, out var denied))
+            return denied;
+
+        var (np, _) = MPerms.Deny.NumInterest(subject);
+        denied = np != 0;
+        MPerms.DCache[subject] = denied;
+        if (MPerms.DCache.Count > MaxDenyPermCacheSize)
+            PruneDenyCache();
+        return denied;
+    }
+
+    internal byte[] MsgHeaderForRouteOrLeaf(byte[] subj, byte[]? reply, RouteTarget rt, INatsAccount? acc)
+    {
+        var msg = new List<byte>(MsgScratchSize)
+        {
+            (byte)(rt.Sub?.Client?.Kind == ClientKind.Leaf ? 'L' : 'R'),
+            (byte)'M',
+            (byte)'S',
+            (byte)'G',
+            (byte)' ',
+        };
+
+        if (acc is not null && rt.Sub?.Client?.Kind == ClientKind.Router)
+        {
+            msg.AddRange(Encoding.ASCII.GetBytes(acc.Name));
+            msg.Add((byte)' ');
+        }
+
+        msg.AddRange(subj);
+        msg.Add((byte)' ');
+
+        if (rt.Qs.Length > 0)
+        {
+            if (reply is { Length: > 0 })
+            {
+                msg.Add((byte)'+');
+                msg.Add((byte)' ');
+                msg.AddRange(reply);
+                msg.Add((byte)' ');
+            }
+            else
+            {
+                msg.Add((byte)'|');
+                msg.Add((byte)' ');
+            }
+            msg.AddRange(rt.Qs);
+            msg.Add((byte)' ');
+        }
+        else if (reply is { Length: > 0 })
+        {
+            msg.AddRange(reply);
+            msg.Add((byte)' ');
+        }
+
+        var pa = ParseCtx.Pa;
+        if (pa.HeaderSize > 0)
+        {
+            msg.AddRange(pa.HeaderBytes ?? Encoding.ASCII.GetBytes(pa.HeaderSize.ToString()));
+            msg.Add((byte)' ');
+            msg.AddRange(pa.SizeBytes ?? Encoding.ASCII.GetBytes(pa.Size.ToString()));
+        }
+        else
+        {
+            msg.AddRange(pa.SizeBytes ?? Encoding.ASCII.GetBytes(pa.Size.ToString()));
+        }
+
+        msg.Add((byte)'\r');
+        msg.Add((byte)'\n');
+        return msg.ToArray();
+    }
+
+    internal byte[] MsgHeader(byte[] subj, byte[]? reply, Subscription sub)
+    {
+        var pa = ParseCtx.Pa;
+        var hasHeader = pa.HeaderSize > 0;
+        var msg = new List<byte>(MsgScratchSize);
+        if (hasHeader)
+            msg.Add((byte)'H');
+        msg.Add((byte)'M');
+        msg.Add((byte)'S');
+        msg.Add((byte)'G');
+        msg.Add((byte)' ');
+        msg.AddRange(subj);
+        msg.Add((byte)' ');
+
+        if (sub.Sid is { Length: > 0 })
+        {
+            msg.AddRange(sub.Sid);
+            msg.Add((byte)' ');
+        }
+
+        if (reply is { Length: > 0 })
+        {
+            msg.AddRange(reply);
+            msg.Add((byte)' ');
+        }
+
+        if (hasHeader)
+        {
+            msg.AddRange(pa.HeaderBytes ?? Encoding.ASCII.GetBytes(pa.HeaderSize.ToString()));
+            msg.Add((byte)' ');
+            msg.AddRange(pa.SizeBytes ?? Encoding.ASCII.GetBytes(pa.Size.ToString()));
+        }
+        else
+        {
+            msg.AddRange(pa.SizeBytes ?? Encoding.ASCII.GetBytes(pa.Size.ToString()));
+        }
+
+        msg.Add((byte)'\r');
+        msg.Add((byte)'\n');
+        return msg.ToArray();
+    }
+
+    internal void StalledWait(ClientConnection producer)
+    {
+        if (producer._in.Tst > StallTotal)
+            return;
+
+        var ttl = OutPb >= OutMp && OutMp > 0 ? StallMax : StallMin;
+        if (producer._in.Tst + ttl > StallTotal)
+            ttl = StallTotal - producer._in.Tst;
+        if (ttl <= TimeSpan.Zero)
+            return;
+
+        var start = DateTime.UtcNow;
+        Thread.Sleep(ttl);
+        producer._in.Tst += DateTime.UtcNow - start;
+    }
+
+    internal bool DeliverMsg(bool prodIsMqtt, Subscription sub, INatsAccount? acc, byte[] subject, byte[] reply, byte[] mh, byte[] msg, bool gwReply)
+    {
+        _ = acc;
+        _ = subject;
+        _ = reply;
+        _ = gwReply;
+
+        if (sub.IsClosed())
+            return false;
+
+        QueueOutbound(mh);
+        QueueOutbound(msg);
+        if (prodIsMqtt)
+            QueueOutbound("\r\n"u8.ToArray());
+
+        AddToPCD(this);
+        return true;
+    }
+
+    internal void AddToPCD(ClientConnection client)
+    {
+        Pcd ??= new Dictionary<ClientConnection, bool>();
+        if (Pcd.TryAdd(client, true))
+            client.OutPb += 0;
+    }
+
+    internal void TrackRemoteReply(string subject, string reply)
+    {
+        _ = subject;
+        _rrTracking ??= new RrTracking
+        {
+            RMap = new Dictionary<string, object>(StringComparer.Ordinal),
+            Lrt = TimeSpan.FromSeconds(1),
+        };
+        _rrTracking.RMap ??= new Dictionary<string, object>(StringComparer.Ordinal);
+        _rrTracking.RMap[reply] = new RespEntry { Time = DateTime.UtcNow };
+    }
+
+    internal void PruneRemoteTracking()
+    {
+        lock (_mu)
+        {
+            if (_rrTracking?.RMap is null || _rrTracking.RMap.Count == 0)
+            {
+                _rrTracking = null;
+                return;
+            }
+
+            var now = DateTime.UtcNow;
+            var ttl = _rrTracking.Lrt <= TimeSpan.Zero ? TimeSpan.FromSeconds(1) : _rrTracking.Lrt;
+            foreach (var key in _rrTracking.RMap.Keys.ToArray())
+            {
+                if (_rrTracking.RMap[key] is RespEntry re && now - re.Time > ttl)
+                    _rrTracking.RMap.Remove(key);
+            }
+
+            if (_rrTracking.RMap.Count == 0)
+            {
+                _rrTracking.Ptmr?.Dispose();
+                _rrTracking = null;
+            }
+        }
+    }
+
+    internal void PruneReplyPerms()
+    {
+        var resp = Perms?.Resp;
+        if (resp is null || Replies is null)
+            return;
+
+        var maxMsgs = resp.MaxMsgs;
+        var ttl = resp.Expires;
+        var now = DateTime.UtcNow;
+
+        foreach (var k in Replies.Keys.ToArray())
+        {
+            var r = Replies[k];
+            if ((maxMsgs > 0 && r.N >= maxMsgs) || (ttl > TimeSpan.Zero && now - r.Time > ttl))
+                Replies.Remove(k);
+        }
+
+        RepliesSincePrune = 0;
+        LastReplyPrune = now;
+    }
+
+    internal void PruneDenyCache()
+    {
+        if (MPerms is null)
+            return;
+
+        var removed = 0;
+        foreach (var subject in MPerms.DCache.Keys.ToArray())
+        {
+            MPerms.DCache.Remove(subject);
+            if (++removed >= PruneSize)
+                break;
+        }
+    }
+
+    internal void PrunePubPermsCache()
+    {
+        if (Perms is null)
+            return;
+
+        for (var i = 0; i < 5; i++)
+        {
+            if (Interlocked.CompareExchange(ref Perms.PRun, 1, 0) != 0)
+                return;
+
+            var removed = 0;
+            foreach (var key in Perms.PCache.Keys.ToArray())
+            {
+                if (Perms.PCache.Remove(key))
+                    removed++;
+                if (removed > PruneSize && Perms.PCache.Count <= MaxPermCacheSize)
+                    break;
+            }
+
+            Interlocked.Add(ref Perms.PcsZ, -removed);
+            Interlocked.Exchange(ref Perms.PRun, 0);
+            if (Perms.PCache.Count <= MaxPermCacheSize)
+                return;
+        }
+    }
+
+    internal bool PubAllowed(string subject) => PubAllowedFullCheck(subject, fullCheck: true, hasLock: false);
+
+    internal bool PubAllowedFullCheck(string subject, bool fullCheck, bool hasLock)
+    {
+        if (Perms is null || (Perms.Pub.Allow is null && Perms.Pub.Deny is null))
+            return true;
+
+        if (Perms.PCache.TryGetValue(subject, out var cached))
+            return cached;
+
+        var checkAllow = !((IsMqtt() || Kind != ClientKind.Client) && subject.StartsWith(MqttPrefix, StringComparison.Ordinal));
+        var allowed = true;
+
+        if (checkAllow && Perms.Pub.Allow is not null)
+        {
+            var (np, _) = Perms.Pub.Allow.NumInterest(subject);
+            allowed = np != 0;
+        }
+
+        if (allowed && Perms.Pub.Deny is not null)
+        {
+            var (np, _) = Perms.Pub.Deny.NumInterest(subject);
+            allowed = np == 0;
+        }
+
+        if (!allowed && fullCheck && Perms.Resp is not null && Replies is not null)
+        {
+            if (hasLock)
+            {
+                if (Replies.TryGetValue(subject, out var resp))
+                {
+                    resp.N++;
+                    if ((Perms.Resp.MaxMsgs > 0 && resp.N > Perms.Resp.MaxMsgs)
+                        || (Perms.Resp.Expires > TimeSpan.Zero && DateTime.UtcNow - resp.Time > Perms.Resp.Expires))
+                    {
+                        Replies.Remove(subject);
+                    }
+                    else
+                    {
+                        Replies[subject] = resp;
+                        allowed = true;
+                    }
+                }
+            }
+            else
+            {
+                lock (_mu)
+                {
+                    if (Replies.TryGetValue(subject, out var resp))
+                    {
+                        resp.N++;
+                        if ((Perms.Resp.MaxMsgs > 0 && resp.N > Perms.Resp.MaxMsgs)
+                            || (Perms.Resp.Expires > TimeSpan.Zero && DateTime.UtcNow - resp.Time > Perms.Resp.Expires))
+                        {
+                            Replies.Remove(subject);
+                        }
+                        else
+                        {
+                            Replies[subject] = resp;
+                            allowed = true;
+                        }
+                    }
+                }
+            }
+        }
+        else
+        {
+            Perms.PCache[subject] = allowed;
+            if (Interlocked.Increment(ref Perms.PcsZ) > MaxPermCacheSize)
+                PrunePubPermsCache();
+        }
+
+        return allowed;
+    }
+
+    internal static bool IsServiceReply(byte[] reply) =>
+        reply.Length > 3 && Encoding.ASCII.GetString(reply, 0, 4) == ReplyPrefix;
+}
diff --git a/dotnet/src/ZB.MOM.NatsNet.Server/ClientConnection.cs b/dotnet/src/ZB.MOM.NatsNet.Server/ClientConnection.cs
index 60bc7d8..2bb31fc 100644
--- a/dotnet/src/ZB.MOM.NatsNet.Server/ClientConnection.cs
+++ b/dotnet/src/ZB.MOM.NatsNet.Server/ClientConnection.cs
@@ -1756,7 +1756,7 @@ public sealed partial class ClientConnection
     // features 471-486: processPub variants, parseSub, processSub, etc.
     // Implemented in full when Server+Account sessions complete.
 
-    // features 487-503: deliverMsg, addToPCD, trackRemoteReply, pruning, pubAllowed, etc.
+    // features 477-496 and 487-503: see ClientConnection.SubscriptionsAndDelivery.cs
 
     // features 512-514: processServiceImport, addSubToRouteTargets, processMsgResults
 
diff --git a/dotnet/tests/ZB.MOM.NatsNet.Server.Tests/ClientConnectionStubFeaturesTests.cs b/dotnet/tests/ZB.MOM.NatsNet.Server.Tests/ClientConnectionStubFeaturesTests.cs
index 57b3e75..592898c 100644
--- a/dotnet/tests/ZB.MOM.NatsNet.Server.Tests/ClientConnectionStubFeaturesTests.cs
+++ b/dotnet/tests/ZB.MOM.NatsNet.Server.Tests/ClientConnectionStubFeaturesTests.cs
@@ -6,7 +6,9 @@ using System.Text;
 using System.Linq;
 using Shouldly;
 using ZB.MOM.NatsNet.Server;
+using ZB.MOM.NatsNet.Server.Auth;
 using ZB.MOM.NatsNet.Server.Internal;
+using ZB.MOM.NatsNet.Server.Internal.DataStructures;
 
 namespace ZB.MOM.NatsNet.Server.Tests;
 
@@ -152,4 +154,89 @@ public sealed class ClientConnectionStubFeaturesTests
         result.sub.ShouldNotBeNull();
         c.Subs.Count.ShouldBe(2);
     }
+
+    [Fact]
+    public void CanSubscribe_WithAllowAndDenyQueues_ShouldMatchExpected()
+    {
+        var c = new ClientConnection(ClientKind.Client)
+        {
+            Perms = new ClientPermissions(),
+        };
+        c.Perms.Sub.Allow = SubscriptionIndex.NewSublistWithCache();
+        c.Perms.Sub.Deny = SubscriptionIndex.NewSublistWithCache();
+        c.Perms.Sub.Allow.Insert(new Subscription
+        {
+            Subject = Encoding.ASCII.GetBytes("foo.*"),
+            Queue = Encoding.ASCII.GetBytes("q"),
+        });
+        c.Perms.Sub.Deny.Insert(new Subscription
+        {
+            Subject = Encoding.ASCII.GetBytes("foo.blocked"),
+        });
+
+        c.CanSubscribe("foo.bar", "q").ShouldBeTrue();
+        c.CanSubscribe("foo.bar", "other").ShouldBeFalse();
+        c.CanSubscribe("foo.blocked").ShouldBeFalse();
+    }
+
+    [Fact]
+    public void ProcessUnsub_WithKnownSid_ShouldRemoveSubscription()
+    {
+        var c = new ClientConnection(ClientKind.Client);
+        c.ParseSub(Encoding.ASCII.GetBytes("foo sid1"), noForward: false).ShouldBeNull();
+        c.Subs.Count.ShouldBe(1);
+
+        c.ProcessUnsub(Encoding.ASCII.GetBytes("sid1")).ShouldBeNull();
+        c.Subs.ShouldNotContainKey("sid1");
+    }
+
+    [Fact]
+    public void MsgHeaderAndRouteHeader_ShouldIncludeSubjectsAndSizes()
+    {
+        var c = new ClientConnection(ClientKind.Client);
+        c.ParseCtx.Pa.HeaderSize = 10;
+        c.ParseCtx.Pa.Size = 30;
+        c.ParseCtx.Pa.HeaderBytes = Encoding.ASCII.GetBytes("10");
+        c.ParseCtx.Pa.SizeBytes = Encoding.ASCII.GetBytes("30");
+
+        var sub = new Subscription { Sid = Encoding.ASCII.GetBytes("22") };
+        var mh = c.MsgHeader(Encoding.ASCII.GetBytes("foo.bar"), Encoding.ASCII.GetBytes("_R_.x"), sub);
+        Encoding.ASCII.GetString(mh).ShouldContain("foo.bar 22 _R_.x");
+        Encoding.ASCII.GetString(mh).ShouldContain("30");
+
+        var routeTarget = new RouteTarget { Sub = sub, Qs = Encoding.ASCII.GetBytes("q1 q2") };
+        var rmh = c.MsgHeaderForRouteOrLeaf(
+            Encoding.ASCII.GetBytes("foo.bar"),
+            Encoding.ASCII.GetBytes("_R_.x"),
+            routeTarget,
+            null);
+        Encoding.ASCII.GetString(rmh).ShouldContain("foo.bar");
+        Encoding.ASCII.GetString(rmh).ShouldContain("q1 q2");
+    }
+
+    [Fact]
+    public void PubAllowedFullCheck_ShouldHonorResponseReplyCache()
+    {
+        var c = new ClientConnection(ClientKind.Client)
+        {
+            Perms = new ClientPermissions
+            {
+                Resp = new ResponsePermission
+                {
+                    MaxMsgs = 2,
+                    Expires = TimeSpan.FromMinutes(1),
+                },
+            },
+            Replies = new Dictionary<string, RespEntry>(StringComparer.Ordinal)
+            {
+                ["_R_.x"] = new RespEntry { Time = DateTime.UtcNow, N = 0 },
+            },
+        };
+        c.Perms.Pub.Deny = SubscriptionIndex.NewSublistWithCache();
+        c.Perms.Pub.Deny.Insert(new Subscription { Subject = Encoding.ASCII.GetBytes(">") });
+
+        c.PubAllowed("_R_.x").ShouldBeTrue();
+        c.PubAllowedFullCheck("_R_.x", fullCheck: true, hasLock: true).ShouldBeTrue();
+        c.PubAllowedFullCheck("_R_.x", fullCheck: true, hasLock: true).ShouldBeFalse();
+    }
 }
diff --git a/dotnet/tests/ZB.MOM.NatsNet.Server.Tests/ClientTests.cs b/dotnet/tests/ZB.MOM.NatsNet.Server.Tests/ClientTests.cs
index cf4a561..0486941 100644
--- a/dotnet/tests/ZB.MOM.NatsNet.Server.Tests/ClientTests.cs
+++ b/dotnet/tests/ZB.MOM.NatsNet.Server.Tests/ClientTests.cs
@@ -189,6 +189,13 @@ public sealed class ClientTests
         c2.SetExpiration(DateTimeOffset.UtcNow.AddSeconds(-1).ToUnixTimeSeconds(), TimeSpan.Zero);
         SpinWait.SpinUntil(c2.IsClosed, TimeSpan.FromSeconds(2)).ShouldBeTrue();
     }
+
+    [Fact]
+    public void ReplyHelpers_ServiceAndReserved_ShouldClassifyPrefixes()
+    {
+        ClientConnection.IsServiceReply(Encoding.ASCII.GetBytes("_R_.A.B")).ShouldBeTrue();
+        ClientConnection.IsServiceReply(Encoding.ASCII.GetBytes("foo.bar")).ShouldBeFalse();
+    }
 }
 
 /// <summary>
diff --git a/porting.db b/porting.db
index baf14ed..a228dc6 100644
Binary files a/porting.db and b/porting.db differ