diff --git a/core/src/main/java/ch/dissem/bitmessage/DefaultMessageListener.java b/core/src/main/java/ch/dissem/bitmessage/DefaultMessageListener.java
index c8eed14..e8be606 100644
--- a/core/src/main/java/ch/dissem/bitmessage/DefaultMessageListener.java
+++ b/core/src/main/java/ch/dissem/bitmessage/DefaultMessageListener.java
@@ -165,8 +165,8 @@ class DefaultMessageListener implements NetworkHandler.MessageListener {
         listener.receive(msg);
         updatePubkey(msg.getFrom(), msg.getFrom().getPubkey());
 
-        if (msg.getType() == Type.MSG && identity.has(Pubkey.Feature.DOES_ACK)) {
-            ObjectMessage ack = plaintext.getAckMessage();
+        if (msg.getType() == Plaintext.Type.MSG && msg.getTo().has(Pubkey.Feature.DOES_ACK)) {
+            ObjectMessage ack = msg.getAckMessage();
             if (ack != null) {
                 ctx.getInventory().storeObject(ack);
                 ctx.getNetworkHandler().offer(ack.getInventoryVector());
diff --git a/core/src/main/java/ch/dissem/bitmessage/InternalContext.java b/core/src/main/java/ch/dissem/bitmessage/InternalContext.java
index 03c6bfc..586adf4 100644
--- a/core/src/main/java/ch/dissem/bitmessage/InternalContext.java
+++ b/core/src/main/java/ch/dissem/bitmessage/InternalContext.java
@@ -16,14 +16,10 @@
 
 package ch.dissem.bitmessage;
 
-import ch.dissem.bitmessage.entity.BitmessageAddress;
-import ch.dissem.bitmessage.entity.Encrypted;
-import ch.dissem.bitmessage.entity.ObjectMessage;
-import ch.dissem.bitmessage.entity.payload.*;
-import ch.dissem.bitmessage.exception.ApplicationException;
 import ch.dissem.bitmessage.entity.*;
 import ch.dissem.bitmessage.entity.payload.*;
 import ch.dissem.bitmessage.entity.valueobject.Label;
+import ch.dissem.bitmessage.exception.ApplicationException;
 import ch.dissem.bitmessage.ports.*;
 import ch.dissem.bitmessage.utils.Singleton;
 import ch.dissem.bitmessage.utils.TTL;
@@ -36,7 +32,6 @@ import java.util.Arrays;
 import java.util.TreeSet;
 
 import static ch.dissem.bitmessage.entity.Plaintext.Status.SENT;
-import static ch.dissem.bitmessage.utils.UnixTime.DAY;
 
 /**
  * The internal context should normally only be used for port implementations. If you need it in your client
@@ -182,11 +177,11 @@ public class InternalContext {
             if (payload instanceof Msg && recipient.has(Pubkey.Feature.DOES_ACK)) {
                 ObjectMessage ackMessage = ((Msg) payload).getPlaintext().getAckMessage();
                 messageCallback.proofOfWorkStarted(payload);
-                security.doProofOfWork(ackMessage, networkNonceTrialsPerByte, networkExtraBytes, new ProofOfWorkEngine.Callback() {
+                cryptography.doProofOfWork(ackMessage, NETWORK_NONCE_TRIALS_PER_BYTE, NETWORK_EXTRA_BYTES, new ProofOfWorkEngine.Callback() {
                     @Override
-                    public void onNonceCalculated(byte[] nonce) {
+                    public void onNonceCalculated(byte[] initialHash, byte[] nonce) {
                         object.encrypt(recipient.getPubkey());
-                        proofOfWorkService.doProofOfWork(to, object);
+                        proofOfWorkService.doProofOfWork(recipient, object);
                     }
                 });
             } else {
@@ -318,7 +313,7 @@ public class InternalContext {
         }
 
         @Override
-        public void onNonceCalculated(byte[] nonce) {
+        public void onNonceCalculated(byte[] initialHash, byte[] nonce) {
             object.setNonce(nonce);
             messageCallback.proofOfWorkCompleted(payload);
             if (payload instanceof PlaintextHolder) {
diff --git a/core/src/main/java/ch/dissem/bitmessage/entity/Plaintext.java b/core/src/main/java/ch/dissem/bitmessage/entity/Plaintext.java
index 01deca8..c7f23ce 100644
--- a/core/src/main/java/ch/dissem/bitmessage/entity/Plaintext.java
+++ b/core/src/main/java/ch/dissem/bitmessage/entity/Plaintext.java
@@ -175,7 +175,7 @@ public class Plaintext implements Streamable {
         if (type == Type.MSG) {
             if (to.has(Pubkey.Feature.DOES_ACK)) {
                 ByteArrayOutputStream ack = new ByteArrayOutputStream();
-                ackMessage.write(ack);
+                getAckMessage().write(ack);
                 byte[] data = ack.toByteArray();
                 Encode.varInt(data.length, out);
                 out.write(data);
diff --git a/domain/src/main/java/ch/dissem/bitmessage/entity/payload/Ack.java b/core/src/main/java/ch/dissem/bitmessage/entity/payload/Ack.java
similarity index 100%
rename from domain/src/main/java/ch/dissem/bitmessage/entity/payload/Ack.java
rename to core/src/main/java/ch/dissem/bitmessage/entity/payload/Ack.java
diff --git a/core/src/test/java/ch/dissem/bitmessage/DefaultMessageListenerTest.java b/core/src/test/java/ch/dissem/bitmessage/DefaultMessageListenerTest.java
index 710bf98..e225924 100644
--- a/core/src/test/java/ch/dissem/bitmessage/DefaultMessageListenerTest.java
+++ b/core/src/test/java/ch/dissem/bitmessage/DefaultMessageListenerTest.java
@@ -24,9 +24,7 @@ import ch.dissem.bitmessage.entity.payload.Broadcast;
 import ch.dissem.bitmessage.entity.payload.GetPubkey;
 import ch.dissem.bitmessage.entity.payload.Msg;
 import ch.dissem.bitmessage.factory.Factory;
-import ch.dissem.bitmessage.ports.AddressRepository;
-import ch.dissem.bitmessage.ports.Labeler;
-import ch.dissem.bitmessage.ports.MessageRepository;
+import ch.dissem.bitmessage.ports.*;
 import ch.dissem.bitmessage.utils.Singleton;
 import ch.dissem.bitmessage.utils.TestBase;
 import ch.dissem.bitmessage.utils.TestUtils;
@@ -51,6 +49,10 @@ public class DefaultMessageListenerTest extends TestBase {
     private AddressRepository addressRepo;
     @Mock
     private MessageRepository messageRepo;
+    @Mock
+    private Inventory inventory;
+    @Mock
+    private NetworkHandler networkHandler;
 
     private InternalContext ctx;
     private DefaultMessageListener listener;
@@ -62,6 +64,8 @@ public class DefaultMessageListenerTest extends TestBase {
         Singleton.initialize(new BouncyCryptography());
         when(ctx.getAddressRepository()).thenReturn(addressRepo);
         when(ctx.getMessageRepository()).thenReturn(messageRepo);
+        when(ctx.getInventory()).thenReturn(inventory);
+        when(ctx.getNetworkHandler()).thenReturn(networkHandler);
 
         listener = new DefaultMessageListener(ctx, mock(Labeler.class), mock(BitmessageContext.Listener.class));
     }
@@ -104,6 +108,7 @@ public class DefaultMessageListenerTest extends TestBase {
     public void ensureIncomingMessageIsSaved() throws Exception {
         BitmessageAddress identity = TestUtils.loadIdentity("BM-2cSqjfJ8xK6UUn5Rw3RpdGQ9RsDkBhWnS8");
         BitmessageAddress contact = new BitmessageAddress(identity.getAddress());
+        contact.setPubkey(identity.getPubkey());
 
         when(addressRepo.getIdentities()).thenReturn(Collections.singletonList(identity));