diff --git a/demo/src/main/java/ch/dissem/bitmessage/demo/Application.java b/demo/src/main/java/ch/dissem/bitmessage/demo/Application.java
index 2f6f9fd..d93c3c8 100644
--- a/demo/src/main/java/ch/dissem/bitmessage/demo/Application.java
+++ b/demo/src/main/java/ch/dissem/bitmessage/demo/Application.java
@@ -22,7 +22,10 @@ import ch.dissem.bitmessage.entity.Plaintext;
 import ch.dissem.bitmessage.entity.payload.Pubkey;
 import ch.dissem.bitmessage.networking.DefaultNetworkHandler;
 import ch.dissem.bitmessage.ports.MemoryNodeRegistry;
-import ch.dissem.bitmessage.repository.*;
+import ch.dissem.bitmessage.repository.JdbcAddressRepository;
+import ch.dissem.bitmessage.repository.JdbcConfig;
+import ch.dissem.bitmessage.repository.JdbcInventory;
+import ch.dissem.bitmessage.repository.JdbcMessageRepository;
 import ch.dissem.bitmessage.security.bc.BouncySecurity;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -50,18 +53,19 @@ public class Application {
                 .networkHandler(new DefaultNetworkHandler())
                 .security(new BouncySecurity())
                 .port(48444)
+                .listener(new BitmessageContext.Listener() {
+                    @Override
+                    public void receive(Plaintext plaintext) {
+                        try {
+                            System.out.println(new String(plaintext.getMessage(), "UTF-8"));
+                        } catch (UnsupportedEncodingException e) {
+                            LOG.error(e.getMessage(), e);
+                        }
+                    }
+                })
                 .build();
 
-        ctx.startup(new BitmessageContext.Listener() {
-            @Override
-            public void receive(Plaintext plaintext) {
-                try {
-                    System.out.println(new String(plaintext.getMessage(), "UTF-8"));
-                } catch (UnsupportedEncodingException e) {
-                    LOG.error(e.getMessage(), e);
-                }
-            }
-        });
+        ctx.startup();
 
         scanner = new Scanner(System.in);
 
diff --git a/domain/src/main/java/ch/dissem/bitmessage/BitmessageContext.java b/domain/src/main/java/ch/dissem/bitmessage/BitmessageContext.java
index 2cd851e..0b3ad1d 100644
--- a/domain/src/main/java/ch/dissem/bitmessage/BitmessageContext.java
+++ b/domain/src/main/java/ch/dissem/bitmessage/BitmessageContext.java
@@ -31,6 +31,7 @@ import ch.dissem.bitmessage.utils.Property;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import java.net.InetAddress;
 import java.util.Arrays;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
@@ -62,10 +63,14 @@ public class BitmessageContext {
 
     private final InternalContext ctx;
 
-    private Listener listener;
+    private final Listener listener;
+    private final NetworkHandler.MessageListener networkListener;
 
     private BitmessageContext(Builder builder) {
         ctx = new InternalContext(builder);
+        listener = builder.listener;
+        networkListener = new DefaultMessageListener(ctx, listener);
+
         // As this thread is used for parts that do POW, which itself uses parallel threads, only
         // one should be executed at any time.
         pool = Executors.newFixedThreadPool(1);
@@ -179,15 +184,22 @@ public class BitmessageContext {
         );
     }
 
-    public void startup(Listener listener) {
-        this.listener = listener;
-        ctx.getNetworkHandler().start(new DefaultMessageListener(ctx, listener));
+    public void startup() {
+        ctx.getNetworkHandler().start(networkListener);
     }
 
     public void shutdown() {
         ctx.getNetworkHandler().stop();
     }
 
+    public void synchronize(InetAddress host, int port, long timeoutInSeconds) {
+        ctx.getNetworkHandler().synchronize(host, port, networkListener, timeoutInSeconds);
+    }
+
+    public void cleanup() {
+        ctx.getInventory().cleanup();
+    }
+
     public boolean isRunning() {
         return ctx.getNetworkHandler().isRunning();
     }
@@ -268,6 +280,7 @@ public class BitmessageContext {
         ProofOfWorkEngine proofOfWorkEngine;
         Security security;
         MessageCallback messageCallback;
+        Listener listener;
 
         public Builder() {
         }
@@ -317,6 +330,11 @@ public class BitmessageContext {
             return this;
         }
 
+        public Builder listener(Listener listener) {
+            this.listener = listener;
+            return this;
+        }
+
         public BitmessageContext build() {
             nonNull("inventory", inventory);
             nonNull("nodeRegistry", nodeRegistry);
diff --git a/domain/src/main/java/ch/dissem/bitmessage/InternalContext.java b/domain/src/main/java/ch/dissem/bitmessage/InternalContext.java
index 403e9c4..6d969bd 100644
--- a/domain/src/main/java/ch/dissem/bitmessage/InternalContext.java
+++ b/domain/src/main/java/ch/dissem/bitmessage/InternalContext.java
@@ -82,7 +82,7 @@ public class InternalContext {
             streams.add(1L);
         }
 
-        init(inventory, nodeRegistry, networkHandler, addressRepository, messageRepository, proofOfWorkEngine);
+        init(security, inventory, nodeRegistry, networkHandler, addressRepository, messageRepository, proofOfWorkEngine);
         for (BitmessageAddress identity : addressRepository.getIdentities()) {
             streams.add(identity.getStream());
         }
diff --git a/domain/src/main/java/ch/dissem/bitmessage/ports/Inventory.java b/domain/src/main/java/ch/dissem/bitmessage/ports/Inventory.java
index 934a4d0..a10d50f 100644
--- a/domain/src/main/java/ch/dissem/bitmessage/ports/Inventory.java
+++ b/domain/src/main/java/ch/dissem/bitmessage/ports/Inventory.java
@@ -36,5 +36,7 @@ public interface Inventory {
 
     void storeObject(ObjectMessage object);
 
+    boolean contains(ObjectMessage object);
+
     void cleanup();
 }
diff --git a/domain/src/main/java/ch/dissem/bitmessage/ports/MemoryNodeRegistry.java b/domain/src/main/java/ch/dissem/bitmessage/ports/MemoryNodeRegistry.java
index 04fa2f9..9c97b87 100644
--- a/domain/src/main/java/ch/dissem/bitmessage/ports/MemoryNodeRegistry.java
+++ b/domain/src/main/java/ch/dissem/bitmessage/ports/MemoryNodeRegistry.java
@@ -34,38 +34,43 @@ import static java.util.Collections.newSetFromMap;
 public class MemoryNodeRegistry implements NodeRegistry {
     private static final Logger LOG = LoggerFactory.getLogger(MemoryNodeRegistry.class);
 
-    private final Map<Long, Set<NetworkAddress>> stableNodes = new HashMap<>();
+    private final Map<Long, Set<NetworkAddress>> stableNodes = new ConcurrentHashMap<>();
     private final Map<Long, Set<NetworkAddress>> knownNodes = new ConcurrentHashMap<>();
 
     public MemoryNodeRegistry() {
-        try (InputStream in = getClass().getClassLoader().getResourceAsStream("nodes.txt")) {
-            Scanner scanner = new Scanner(in);
-            long stream = 0;
-            Set<NetworkAddress> streamSet = null;
-            while (scanner.hasNext()) {
-                try {
-                    String line = scanner.nextLine().trim();
-                    if (line.startsWith("#") || line.isEmpty()) {
-                        // Ignore
-                        continue;
-                    }
-                    if (line.startsWith("[stream")) {
-                        stream = Long.parseLong(line.substring(8, line.lastIndexOf(']')));
-                        streamSet = new HashSet<>();
-                        stableNodes.put(stream, streamSet);
-                    } else if (streamSet != null) {
-                        int portIndex = line.lastIndexOf(':');
-                        InetAddress inetAddress = InetAddress.getByName(line.substring(0, portIndex));
-                        int port = Integer.valueOf(line.substring(portIndex + 1));
-                        streamSet.add(new NetworkAddress.Builder().ip(inetAddress).port(port).stream(stream).build());
+        new Thread(new Runnable() {
+            @Override
+            public void run() {
+                try (InputStream in = getClass().getClassLoader().getResourceAsStream("nodes.txt")) {
+                    Scanner scanner = new Scanner(in);
+                    long stream = 0;
+                    Set<NetworkAddress> streamSet = null;
+                    while (scanner.hasNext()) {
+                        try {
+                            String line = scanner.nextLine().trim();
+                            if (line.startsWith("#") || line.isEmpty()) {
+                                // Ignore
+                                continue;
+                            }
+                            if (line.startsWith("[stream")) {
+                                stream = Long.parseLong(line.substring(8, line.lastIndexOf(']')));
+                                streamSet = new HashSet<>();
+                                stableNodes.put(stream, streamSet);
+                            } else if (streamSet != null) {
+                                int portIndex = line.lastIndexOf(':');
+                                InetAddress inetAddress = InetAddress.getByName(line.substring(0, portIndex));
+                                int port = Integer.valueOf(line.substring(portIndex + 1));
+                                streamSet.add(new NetworkAddress.Builder().ip(inetAddress).port(port).stream(stream).build());
+                            }
+                        } catch (IOException e) {
+                            LOG.warn(e.getMessage(), e);
+                        }
                     }
                 } catch (IOException e) {
-                    LOG.warn(e.getMessage(), e);
+                    throw new RuntimeException(e);
                 }
             }
-        } catch (IOException e) {
-            throw new RuntimeException(e);
-        }
+        }, "node registry initializer").start();
     }
 
     @Override
diff --git a/domain/src/main/java/ch/dissem/bitmessage/ports/MessageRepository.java b/domain/src/main/java/ch/dissem/bitmessage/ports/MessageRepository.java
index 6d8970b..af7b2bc 100644
--- a/domain/src/main/java/ch/dissem/bitmessage/ports/MessageRepository.java
+++ b/domain/src/main/java/ch/dissem/bitmessage/ports/MessageRepository.java
@@ -28,6 +28,8 @@ public interface MessageRepository {
 
     List<Label> getLabels(Label.Type... types);
 
+    int countUnread(Label label);
+
     List<Plaintext> findMessages(Label label);
 
     List<Plaintext> findMessages(Status status);
diff --git a/domain/src/main/resources/nodes.txt b/domain/src/main/resources/nodes.txt
index b728ba5..ab2b69c 100644
--- a/domain/src/main/resources/nodes.txt
+++ b/domain/src/main/resources/nodes.txt
@@ -1,15 +1,19 @@
 [stream 1]
 
-[2604:2000:1380:9f:82e:148b:2746:d0c7]:8080
 5.45.99.75:8444
 75.167.159.54:8444
 95.165.168.168:8444
 85.180.139.241:8444
-158.222.211.81:8080
 178.62.12.187:8448
+
+[2604:2000:1380:9f:82e:148b:2746:d0c7]:8080
+158.222.211.81:8080
 24.188.198.204:8111
 109.147.204.113:1195
 178.11.46.221:8444
 
+# Add named nodes at the end, as resolving them might take time
+dissem.ch:8444
+
 [stream 2]
 # none yet
\ No newline at end of file
diff --git a/networking/src/main/java/ch/dissem/bitmessage/networking/Connection.java b/networking/src/main/java/ch/dissem/bitmessage/networking/Connection.java
index 400bada..5015094 100644
--- a/networking/src/main/java/ch/dissem/bitmessage/networking/Connection.java
+++ b/networking/src/main/java/ch/dissem/bitmessage/networking/Connection.java
@@ -310,6 +310,8 @@ public class Connection implements Runnable {
                 try {
                     LOG.debug("Received object " + objectMessage.getInventoryVector());
                     security().checkProofOfWork(objectMessage, ctx.getNetworkNonceTrialsPerByte(), ctx.getNetworkExtraBytes());
+                    if (ctx.getInventory().contains(objectMessage))
+                        break;
                     listener.receive(objectMessage);
                     ctx.getInventory().storeObject(objectMessage);
                     // offer object to some random nodes so it gets distributed throughout the network:
diff --git a/networking/src/test/java/ch/dissem/bitmessage/networking/NetworkHandlerTest.java b/networking/src/test/java/ch/dissem/bitmessage/networking/NetworkHandlerTest.java
index 7beca24..7ba8fc4 100644
--- a/networking/src/test/java/ch/dissem/bitmessage/networking/NetworkHandlerTest.java
+++ b/networking/src/test/java/ch/dissem/bitmessage/networking/NetworkHandlerTest.java
@@ -55,8 +55,9 @@ public class NetworkHandlerTest {
                 .nodeRegistry(new TestNodeRegistry())
                 .networkHandler(new DefaultNetworkHandler())
                 .security(new BouncySecurity())
+                .listener(Mockito.mock(BitmessageContext.Listener.class))
                 .build();
-        peer.startup(Mockito.mock(BitmessageContext.Listener.class));
+        peer.startup();
 
         nodeInventory = new TestInventory();
         networkHandler = new DefaultNetworkHandler();
@@ -68,13 +69,14 @@ public class NetworkHandlerTest {
                 .nodeRegistry(new TestNodeRegistry(localhost))
                 .networkHandler(networkHandler)
                 .security(new BouncySecurity())
+                .listener(Mockito.mock(BitmessageContext.Listener.class))
                 .build();
     }
 
     @Test(timeout = 20_000)
     public void ensureNodesAreConnecting() {
         try {
-            node.startup(Mockito.mock(BitmessageContext.Listener.class));
+            node.startup();
             Property status;
             do {
                 Thread.yield();
diff --git a/networking/src/test/java/ch/dissem/bitmessage/networking/TestInventory.java b/networking/src/test/java/ch/dissem/bitmessage/networking/TestInventory.java
index 040e730..cefe316 100644
--- a/networking/src/test/java/ch/dissem/bitmessage/networking/TestInventory.java
+++ b/networking/src/test/java/ch/dissem/bitmessage/networking/TestInventory.java
@@ -60,6 +60,11 @@ public class TestInventory implements Inventory {
         inventory.put(object.getInventoryVector(), object);
     }
 
+    @Override
+    public boolean contains(ObjectMessage object) {
+        return inventory.containsKey(object.getInventoryVector());
+    }
+
     @Override
     public void cleanup() {
 
diff --git a/repositories/src/main/java/ch/dissem/bitmessage/repository/JdbcInventory.java b/repositories/src/main/java/ch/dissem/bitmessage/repository/JdbcInventory.java
index 98034ee..4adc532 100644
--- a/repositories/src/main/java/ch/dissem/bitmessage/repository/JdbcInventory.java
+++ b/repositories/src/main/java/ch/dissem/bitmessage/repository/JdbcInventory.java
@@ -24,7 +24,6 @@ import ch.dissem.bitmessage.ports.Inventory;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-import java.io.ByteArrayInputStream;
 import java.sql.*;
 import java.util.LinkedList;
 import java.util.List;
@@ -139,6 +138,23 @@ public class JdbcInventory extends JdbcHelper implements Inventory {
         }
     }
 
+    @Override
+    public boolean contains(ObjectMessage object) {
+        try (Connection connection = config.getConnection()) {
+            Statement stmt = connection.createStatement();
+            ResultSet rs = stmt.executeQuery("SELECT count(1) FROM Inventory WHERE hash = X'"
+                    + object.getInventoryVector() + "'");
+            if (rs.next()) {
+                return rs.getInt(1) > 0;
+            } else {
+                throw new RuntimeException("Couldn't query if inventory contains " + object.getInventoryVector());
+            }
+        } catch (Exception e) {
+            LOG.error(e.getMessage(), e);
+            throw new RuntimeException(e);
+        }
+    }
+
     @Override
     public void cleanup() {
         try (Connection connection = config.getConnection()) {
diff --git a/repositories/src/main/java/ch/dissem/bitmessage/repository/JdbcMessageRepository.java b/repositories/src/main/java/ch/dissem/bitmessage/repository/JdbcMessageRepository.java
index 759012b..4599b79 100644
--- a/repositories/src/main/java/ch/dissem/bitmessage/repository/JdbcMessageRepository.java
+++ b/repositories/src/main/java/ch/dissem/bitmessage/repository/JdbcMessageRepository.java
@@ -25,7 +25,6 @@ import ch.dissem.bitmessage.ports.MessageRepository;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-import java.io.ByteArrayInputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.sql.*;
@@ -86,6 +85,29 @@ public class JdbcMessageRepository extends JdbcHelper implements MessageReposito
         return result;
     }
 
+    @Override
+    public int countUnread(Label label) {
+        String where;
+        if (label != null) {
+            where = "id IN (SELECT message_id FROM Message_Label WHERE label_id=" + label.getId() + ") AND ";
+        } else {
+            where = "";
+        }
+        where += "id IN (SELECT message_id FROM Message_Label WHERE label_id IN (" +
+                "SELECT id FROM Label WHERE type = '" + Label.Type.UNREAD.name() + "'))";
+
+        try (Connection connection = config.getConnection()) {
+            Statement stmt = connection.createStatement();
+            ResultSet rs = stmt.executeQuery("SELECT count(*) FROM Message WHERE " + where);
+            if (rs.next()) {
+                return rs.getInt(1);
+            }
+        } catch (SQLException e) {
+            LOG.error(e.getMessage(), e);
+        }
+        return 0;
+    }
+
     @Override
     public List<Plaintext> findMessages(Label label) {
         return find("id IN (SELECT message_id FROM Message_Label WHERE label_id=" + label.getId() + ")");
@@ -230,8 +252,20 @@ public class JdbcMessageRepository extends JdbcHelper implements MessageReposito
     @Override
     public void remove(Plaintext message) {
         try (Connection connection = config.getConnection()) {
-            Statement stmt = connection.createStatement();
-            stmt.executeUpdate("DELETE FROM Message WHERE id = " + message.getId());
+            try {
+                connection.setAutoCommit(false);
+                Statement stmt = connection.createStatement();
+                stmt.executeUpdate("DELETE FROM Message_Label WHERE message_id = " + message.getId());
+                stmt.executeUpdate("DELETE FROM Message WHERE id = " + message.getId());
+                connection.commit();
+            } catch (SQLException e) {
+                try {
+                    connection.rollback();
+                } catch (SQLException e1) {
+                    LOG.debug(e1.getMessage(), e);
+                }
+                LOG.error(e.getMessage(), e);
+            }
         } catch (SQLException e) {
             LOG.error(e.getMessage(), e);
         }
diff --git a/repositories/src/test/java/ch/dissem/bitmessage/repository/JdbcInventoryTest.java b/repositories/src/test/java/ch/dissem/bitmessage/repository/JdbcInventoryTest.java
index 3954766..6f31299 100644
--- a/repositories/src/test/java/ch/dissem/bitmessage/repository/JdbcInventoryTest.java
+++ b/repositories/src/test/java/ch/dissem/bitmessage/repository/JdbcInventoryTest.java
@@ -110,6 +110,17 @@ public class JdbcInventoryTest extends TestBase {
         assertNotNull(inventory.getObject(object.getInventoryVector()));
     }
 
+    @Test
+    public void testContains() {
+        ObjectMessage object = getObjectMessage(5, 0, getGetPubkey());
+
+        assertFalse(inventory.contains(object));
+
+        inventory.storeObject(object);
+
+        assertTrue(inventory.contains(object));
+    }
+
     @Test
     public void testCleanup() throws Exception {
         assertNotNull(inventory.getObject(inventoryVectorIgnore));