diff --git a/pom.xml b/pom.xml
index bf35cbb..0b5487d 100644
--- a/pom.xml
+++ b/pom.xml
@@ -28,7 +28,7 @@
 		<dependency>
 			<groupId>com.github.informatik-ag-ngl</groupId>
 			<artifactId>envoy-common</artifactId>
-			<version>e5c67b8</version>
+			<version>develop-SNAPSHOT</version>
 		</dependency>
 	</dependencies>
 
diff --git a/src/main/java/envoy/client/Client.java b/src/main/java/envoy/client/Client.java
index 4885a92..935669f 100644
--- a/src/main/java/envoy/client/Client.java
+++ b/src/main/java/envoy/client/Client.java
@@ -11,6 +11,7 @@ import javax.naming.TimeLimitExceededException;
 
 import envoy.client.util.EnvoyLog;
 import envoy.data.*;
+import envoy.event.IdGeneratorRequest;
 import envoy.util.SerializationUtils;
 
 /**
@@ -45,11 +46,13 @@ public class Client implements Closeable {
 	 * an exception is thrown.
 	 *
 	 * @param credentials the login credentials of the user
+	 * @param localDB     the local database used to persist the current
+	 *                    {@link IdGenerator}
 	 * @throws Exception if the online mode could not be entered or the request
 	 *                   failed for some other reason
 	 * @since Envoy v0.2-alpha
 	 */
-	public void onlineInit(LoginCredentials credentials) throws Exception {
+	public void onlineInit(LoginCredentials credentials, LocalDB localDB) throws Exception {
 		// Establish TCP connection
 		logger.info(String.format("Attempting connection to server %s:%d...", config.getServer(), config.getPort()));
 		socket = new Socket(config.getServer(), config.getPort());
@@ -84,21 +87,38 @@ public class Client implements Closeable {
 
 		// Register processors for message and status handling
 		receiver.registerProcessor(Message.class, new ReceivedMessageProcessor());
+		// TODO: Status handling
+
+		// Process message ID generation
+		receiver.registerProcessor(IdGenerator.class, localDB::setIdGenerator);
+
+		// Request a generator if none is present
+		if (!localDB.hasIdGenerator() || !localDB.getIdGenerator().hasNext()) requestIdGenerator();
 	}
 
 	/**
 	 * Sends a message to the server.
-	 * 
+	 *
 	 * @param message the message to send
 	 * @throws IOException if the message does not reach the server
 	 * @since Envoy v0.3-alpha
 	 */
 	public void sendMessage(Message message) throws IOException {
-		checkOnline();
-		SerializationUtils.writeBytesWithLength(message, socket.getOutputStream());
+		writeObject(message);
 		message.nextStatus();
 	}
 
+	/**
+	 * Requests a new {@link IdGenerator} from the server.
+	 *
+	 * @throws IOException if the request does not reach the server
+	 * @since Envoy v0.3-alpha
+	 */
+	public void requestIdGenerator() throws IOException {
+		logger.info("Requesting new id generator...");
+		writeObject(new IdGeneratorRequest());
+	}
+
 	/**
 	 * @return a {@code Map<String, User>} of all users on the server with their
 	 *         user names as keys
@@ -114,6 +134,11 @@ public class Client implements Closeable {
 	@Override
 	public void close() throws IOException { if (online) socket.close(); }
 
+	private void writeObject(Object obj) throws IOException {
+		checkOnline();
+		SerializationUtils.writeBytesWithLength(obj, socket.getOutputStream());
+	}
+
 	private void checkOnline() { if (!online) throw new IllegalStateException("Client is not online"); }
 
 	/**
diff --git a/src/main/java/envoy/client/LocalDB.java b/src/main/java/envoy/client/LocalDB.java
index 2c40e65..7511d41 100644
--- a/src/main/java/envoy/client/LocalDB.java
+++ b/src/main/java/envoy/client/LocalDB.java
@@ -4,10 +4,15 @@ import java.io.File;
 import java.io.IOException;
 import java.util.*;
 
+import envoy.data.IdGenerator;
 import envoy.data.User;
 import envoy.util.SerializationUtils;
 
 /**
+ * Stored information about the current {@link User} and their {@link Chat}s.
+ * For message ID generation a {@link IdGenerator} is stored as well.
+ * These object are persisted inside a folder of the local file system.<br>
+ * <br>
  * Project: <strong>envoy-client</strong><br>
  * File: <strong>LocalDB.java</strong><br>
  * Created: <strong>27.10.2019</strong><br>
@@ -18,10 +23,11 @@ import envoy.util.SerializationUtils;
  */
 public class LocalDB {
 
-	private File				localDBDir, localDBFile, usersFile;
+	private File				localDBDir, localDBFile, usersFile, idGeneratorFile;
 	private User				user;
 	private Map<String, User>	users	= new HashMap<>();
 	private List<Chat>			chats	= new ArrayList<>();
+	private IdGenerator			idGenerator;
 
 	/**
 	 * Constructs an empty local database. To serialize any chats to the file
@@ -37,7 +43,8 @@ public class LocalDB {
 		// Initialize local database directory
 		if (localDBDir.exists() && !localDBDir.isDirectory())
 			throw new IOException(String.format("LocalDBDir '%s' is not a directory!", localDBDir.getAbsolutePath()));
-		usersFile = new File(localDBDir, "users.db");
+		usersFile		= new File(localDBDir, "users.db");
+		idGeneratorFile	= new File(localDBDir, "id_generator.db");
 	}
 
 	/**
@@ -53,7 +60,8 @@ public class LocalDB {
 
 	/**
 	 * Stores all users to the local database. If the client user is specified, the
-	 * chats related to this user are stored as well.
+	 * chats related to this user are stored as well. The message id generator will
+	 * also be saved if present.
 	 *
 	 * @throws IOException if something went wrong during saving
 	 * @since Envoy v0.1-alpha
@@ -63,12 +71,15 @@ public class LocalDB {
 		SerializationUtils.write(usersFile, users);
 
 		// Save chats
-		SerializationUtils.write(localDBFile, chats);
+		if (user != null) SerializationUtils.write(localDBFile, chats);
+
+		// Save id generator
+		if (hasIdGenerator()) SerializationUtils.write(idGeneratorFile, idGenerator);
 	}
 
 	/**
 	 * Loads all users that are stored in the local database.
-	 * 
+	 *
 	 * @throws IOException            if the loading process failed
 	 * @throws ClassNotFoundException if the loading process failed
 	 * @since Envoy v0.2-alpha
@@ -77,13 +88,25 @@ public class LocalDB {
 
 	/**
 	 * Loads all chats saved by Envoy for the client user.
-	 * 
+	 *
 	 * @throws IOException            if the loading process failed
 	 * @throws ClassNotFoundException if the loading process failed
 	 * @since Envoy v0.1-alpha
 	 */
 	public void loadChats() throws ClassNotFoundException, IOException { chats = SerializationUtils.read(localDBFile, ArrayList.class); }
 
+	/**
+	 * Loads the message ID generator that is stored in the local database. If the
+	 * file is not found, the exception is ignored.
+	 *
+	 * @since Envoy v0.3-alpha
+	 */
+	public void loadIdGenerator() {
+		try {
+			idGenerator = SerializationUtils.read(idGeneratorFile, IdGenerator.class);
+		} catch (ClassNotFoundException | IOException e) {}
+	}
+
 	/**
 	 * @return a {@code Map<String, User>} of all users stored locally with their
 	 *         user names as keys
@@ -119,4 +142,22 @@ public class LocalDB {
 	 * @since Envoy v0.2-alpha
 	 */
 	public void setUser(User user) { this.user = user; }
+
+	/**
+	 * @return the message ID generator
+	 * @since Envoy v0.3-alpha
+	 */
+	public IdGenerator getIdGenerator() { return idGenerator; }
+
+	/**
+	 * @param idGenerator the message ID generator to set
+	 * @since Envoy v0.3-alpha
+	 */
+	public void setIdGenerator(IdGenerator idGenerator) { this.idGenerator = idGenerator; }
+
+	/**
+	 * @return {@code true} if an {@link IdGenerator} is present
+	 * @since Envoy v0.3-alpha
+	 */
+	public boolean hasIdGenerator() { return idGenerator != null; }
 }
\ No newline at end of file
diff --git a/src/main/java/envoy/client/ui/ChatWindow.java b/src/main/java/envoy/client/ui/ChatWindow.java
index 3c4cdee..51c7d7f 100644
--- a/src/main/java/envoy/client/ui/ChatWindow.java
+++ b/src/main/java/envoy/client/ui/ChatWindow.java
@@ -10,6 +10,7 @@ import javax.swing.*;
 import javax.swing.border.EmptyBorder;
 
 import envoy.client.*;
+import envoy.client.event.MessageCreationEvent;
 import envoy.client.event.ThemeChangeEvent;
 import envoy.client.ui.list.ComponentList;
 import envoy.client.ui.settings.SettingsScreen;
@@ -175,7 +176,9 @@ public class ChatWindow extends JFrame {
 
 				messageList.setModel(currentChat.getModel());
 				scrollPane.setChatOpened(true);
-				contentPane.revalidate();
+
+				revalidate();
+				repaint();
 			}
 		});
 
@@ -194,13 +197,20 @@ public class ChatWindow extends JFrame {
 		contentPane.add(userList, gbc_userList);
 		contentPane.revalidate();
 
+		// Listen to theme changes
 		EventBus.getInstance().register(ThemeChangeEvent.class, (evt) -> applyTheme((Theme) evt.get()));
 
+		// Listen to received messages
+		EventBus.getInstance().register(MessageCreationEvent.class, (evt) -> {
+			Message message = ((MessageCreationEvent) evt).get();
+			localDB.getChats().stream().filter(c -> c.getRecipient().getId() == message.getRecipientId()).findFirst().get().appendMessage(message);
+		});
+
 		contentPane.revalidate();
 	}
 
 	/**
-	 * Used to immediately reload the ChatWindow when settings were changed.
+	 * Used to immediately reload the {@link ChatWindow} when settings were changed.
 	 *
 	 * @param theme the theme to change colors into
 	 * @since Envoy v0.2-alpha
@@ -247,7 +257,7 @@ public class ChatWindow extends JFrame {
 		if (!messageEnterTextArea.getText().isEmpty()) try {
 
 			// Create message
-			final Message message = new MessageBuilder(localDB.getUser().getId(), currentChat.getRecipient().getId())
+			final Message message = new MessageBuilder(localDB.getUser().getId(), currentChat.getRecipient().getId(), localDB.getIdGenerator())
 				.setText(messageEnterTextArea.getText())
 				.build();
 
@@ -262,12 +272,17 @@ public class ChatWindow extends JFrame {
 			// Clear text field
 			messageEnterTextArea.setText("");
 
+			// Update UI
 			revalidate();
 			repaint();
+
+			// Request a new id generator if all ids were used
+			if (!localDB.getIdGenerator().hasNext()) client.requestIdGenerator();
+
 		} catch (Exception e) {
 			JOptionPane.showMessageDialog(this,
-					"An exception occured while sending a message. See the log for more details.",
-					"Exception occured",
+					"Error sending message:\n" + e.toString(),
+					"Message sending error",
 					JOptionPane.ERROR_MESSAGE);
 			e.printStackTrace();
 		}
diff --git a/src/main/java/envoy/client/ui/Startup.java b/src/main/java/envoy/client/ui/Startup.java
index 3e4692d..2fb9a3a 100644
--- a/src/main/java/envoy/client/ui/Startup.java
+++ b/src/main/java/envoy/client/ui/Startup.java
@@ -62,7 +62,7 @@ public class Startup {
 			if (!config.isInitialized()) throw new EnvoyException("Server or port are not defined");
 		} catch (Exception e) {
 			JOptionPane
-				.showMessageDialog(null, "Error loading configuration values: \n" + e.toString(), "Configuration error", JOptionPane.ERROR_MESSAGE);
+				.showMessageDialog(null, "Error loading configuration values:\n" + e.toString(), "Configuration error", JOptionPane.ERROR_MESSAGE);
 			System.exit(1);
 			e.printStackTrace();
 		}
@@ -97,7 +97,8 @@ public class Startup {
 		Client client = new Client();
 		try {
 			// Try entering online mode first
-			client.onlineInit(credentials);
+			localDB.loadIdGenerator();
+			client.onlineInit(credentials, localDB);
 		} catch (Exception e1) {
 			logger.warning("Could not connect to server. Trying offline mode...");
 			e1.printStackTrace();