diff --git a/pom.xml b/pom.xml
index 5b81ded..48a6be0 100644
--- a/pom.xml
+++ b/pom.xml
@@ -33,6 +33,11 @@
 			<artifactId>hibernate-core</artifactId>
 			<version>5.4.10.Final</version>
 		</dependency>
+		<dependency>
+			<groupId>org.postgresql</groupId>
+			<artifactId>postgresql</artifactId>
+			<version>42.2.9</version>
+		</dependency>
 	</dependencies>
 
 	<build>
diff --git a/src/main/java/envoy/server/LoginCredentialProcessor.java b/src/main/java/envoy/server/LoginCredentialProcessor.java
index 0a84edf..89261cf 100644
--- a/src/main/java/envoy/server/LoginCredentialProcessor.java
+++ b/src/main/java/envoy/server/LoginCredentialProcessor.java
@@ -1,7 +1,12 @@
 package envoy.server;
 
+import java.io.IOException;
+import java.util.ArrayList;
+
+import envoy.data.Contacts;
 import envoy.data.LoginCredentials;
 import envoy.data.User;
+import envoy.server.net.ObjectWriteProxy;
 
 /**
  * This {@link ObjectProcessor} handles {@link LoginCredentials}.<br>
@@ -13,7 +18,7 @@ import envoy.data.User;
  * @author Kai S. K. Engelbart
  * @since Envoy Server Standalone v0.1-alpha
  */
-public class LoginCredentialProcessor implements ObjectProcessor<LoginCredentials, User> {
+public class LoginCredentialProcessor implements ObjectProcessor<LoginCredentials> {
 
 	// TODO: Acquire user IDs from database
 	private static long currentUserId = 1;
@@ -22,10 +27,20 @@ public class LoginCredentialProcessor implements ObjectProcessor<LoginCredential
 	public Class<LoginCredentials> getInputClass() { return LoginCredentials.class; }
 
 	@Override
-	public User process(LoginCredentials input, long socketId) {
+	public void process(LoginCredentials input, long socketId, ObjectWriteProxy writeProxy) throws IOException {
 		System.out.println(String.format("Received login credentials %s from socket ID %d", input, socketId));
+
+		// Create user
 		User user = new User(currentUserId++, input.getName());
 		ConnectionManager.getInstance().registerUser(socketId, user.getId());
-		return user;
+
+		// Create contacts
+		Contacts contacts = new Contacts(user.getId(), new ArrayList<>());
+
+		// Complete handshake
+		System.out.println("Sending user...");
+		writeProxy.write(socketId, user);
+		System.out.println("Sending contacts...");
+		writeProxy.write(socketId, contacts);
 	}
 }
diff --git a/src/main/java/envoy/server/MessageProcessor.java b/src/main/java/envoy/server/MessageProcessor.java
index 8d80e53..3e2f139 100644
--- a/src/main/java/envoy/server/MessageProcessor.java
+++ b/src/main/java/envoy/server/MessageProcessor.java
@@ -1,6 +1,7 @@
 package envoy.server;
 
 import envoy.data.Message;
+import envoy.server.net.ObjectWriteProxy;
 
 /**
  * This {@link ObjectProcessor} handles incoming {@link Message}s.<br>
@@ -12,13 +13,13 @@ import envoy.data.Message;
  * @author Kai S. K. Engelbart
  * @since Envoy Server Standalone v0.1-alpha
  */
-public class MessageProcessor implements ObjectProcessor<Message, Void> {
+public class MessageProcessor implements ObjectProcessor<Message> {
 
 	@Override
 	public Class<Message> getInputClass() { return Message.class; }
 
 	@Override
-	public Void process(Message message, long socketId) {
+	public void process(Message message, long socketId, ObjectWriteProxy writeProxy) {
 
 		// TODO: Send message to recipient if online
 		ConnectionManager connectionManager = ConnectionManager.getInstance();
@@ -27,6 +28,5 @@ public class MessageProcessor implements ObjectProcessor<Message, Void> {
 		}
 
 		// TODO: Add message to database
-		return null;
 	}
 }
diff --git a/src/main/java/envoy/server/ObjectProcessor.java b/src/main/java/envoy/server/ObjectProcessor.java
index 07c0480..0221fc0 100644
--- a/src/main/java/envoy/server/ObjectProcessor.java
+++ b/src/main/java/envoy/server/ObjectProcessor.java
@@ -1,5 +1,9 @@
 package envoy.server;
 
+import java.io.IOException;
+
+import envoy.server.net.ObjectWriteProxy;
+
 /**
  * This interface defines methods for processing objects of a specific
  * type incoming from a client.<br>
@@ -10,13 +14,12 @@ package envoy.server;
  *
  * @author Kai S. K. Engelbart
  * @param <T> type of the request object
- * @param <U> type of the response object
  * @since Envoy Server Standalone v0.1-alpha
  */
-public interface ObjectProcessor<T, U> {
+public interface ObjectProcessor<T> {
 
 	/**
-	 * @return the Class of the request object
+	 * @return the class of the request object
 	 * @since Envoy Server Standalone v0.1-alpha
 	 */
 	Class<T> getInputClass();
@@ -27,5 +30,5 @@ public interface ObjectProcessor<T, U> {
 	 * @return the response object
 	 * @since Envoy Server Standalone v0.1-alpha
 	 */
-	U process(T input, long socketId);
+	void process(T input, long socketId, ObjectWriteProxy writeProxy) throws IOException;
 }
\ No newline at end of file
diff --git a/src/main/java/envoy/server/data/Message.java b/src/main/java/envoy/server/data/Message.java
index 19e25a6..af7f612 100644
--- a/src/main/java/envoy/server/data/Message.java
+++ b/src/main/java/envoy/server/data/Message.java
@@ -4,6 +4,7 @@ import java.util.Date;
 
 import javax.persistence.Entity;
 import javax.persistence.Id;
+import javax.persistence.ManyToOne;
 import javax.persistence.NamedQueries;
 import javax.persistence.NamedQuery;
 import javax.persistence.Table;
@@ -28,8 +29,12 @@ import envoy.data.MessageBuilder;
 @Entity
 @Table(name = "messages")
 @NamedQueries(
-	{ @NamedQuery(query = "SELECT m FROM Message m WHERE m.recipient =:recipient AND m.state = 1", name = "getUnreadMessages"), @NamedQuery(
-		query = "SELECT m FROM Message m WHERE m.sender =:sender AND m.state = :state",
+	{ @NamedQuery(
+		query = "SELECT m FROM Message m WHERE m.recipient =:recipient AND m.status = envoy.data.Message$MessageStatus.SENT",
+		name = "getUnreadMessages"
+	),
+			@NamedQuery(
+				query = "SELECT m FROM Message m WHERE m.sender =:sender AND m.status = :status",
 		name = "find read messages"//TODO do we need this namedQuery?
 	), @NamedQuery(query = "SELECT m FROM Message m WHERE m.id = :messageId", name = "get message") }//TODO do we need this namedQuery?
 )
@@ -37,13 +42,22 @@ public class Message {
 
 	@Id
 	private long								id;
-	private User								sender, recipient;
+
+	@ManyToOne
+	private User sender;
+
+	@ManyToOne
+	private User recipient;
+
 	@Temporal(TemporalType.TIMESTAMP)
 	private Date								creationDate;
+
 	@Temporal(TemporalType.TIMESTAMP)
 	private Date								receivedDate;
+
 	@Temporal(TemporalType.TIMESTAMP)
 	private Date								readDate;
+
 	private envoy.data.Message.MessageStatus	status;
 	private String								text;
 	private byte[]								attachment;
diff --git a/src/main/java/envoy/server/data/User.java b/src/main/java/envoy/server/data/User.java
index e0de15f..40e25c7 100644
--- a/src/main/java/envoy/server/data/User.java
+++ b/src/main/java/envoy/server/data/User.java
@@ -3,6 +3,7 @@ package envoy.server.data;
 import java.util.Date;
 import java.util.List;
 
+import javax.persistence.ElementCollection;
 import javax.persistence.Entity;
 import javax.persistence.GeneratedValue;
 import javax.persistence.GenerationType;
@@ -27,7 +28,7 @@ import javax.persistence.TemporalType;
  */
 @Entity
 @Table(name = "users")
-@NamedQuery(query = "SELECT u FROM DBUser u WHERE u.id = :id", name = "getUserById")
+@NamedQuery(query = "SELECT u FROM User u WHERE u.id = :id", name = "getUserById")
 public class User {
 
 	@Id
@@ -35,9 +36,12 @@ public class User {
 	private long						id;
 	private String						name;
 	private byte[]						passwordHash;
+
 	@Temporal(TemporalType.TIMESTAMP)
 	private Date						lastSeen;
 	private envoy.data.User.UserStatus	status;
+
+	@ElementCollection
 	private List<User>					contacts;
 
 	/**
diff --git a/src/main/java/envoy/server/net/ObjectMessageProcessor.java b/src/main/java/envoy/server/net/ObjectMessageProcessor.java
index 1bf707f..47dae57 100644
--- a/src/main/java/envoy/server/net/ObjectMessageProcessor.java
+++ b/src/main/java/envoy/server/net/ObjectMessageProcessor.java
@@ -1,10 +1,8 @@
 package envoy.server.net;
 
 import java.io.ByteArrayInputStream;
-import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.io.ObjectInputStream;
-import java.io.ObjectOutputStream;
 import java.util.Set;
 
 import com.jenkov.nioserver.IMessageProcessor;
@@ -25,7 +23,7 @@ import envoy.server.ObjectProcessor;
  */
 public class ObjectMessageProcessor implements IMessageProcessor {
 
-	private final Set<ObjectProcessor<?, ?>>	processors;
+	private final Set<ObjectProcessor<?>> processors;
 
 	/**
 	 * The constructor to set the {@link ObjectProcessor}s.
@@ -33,9 +31,7 @@ public class ObjectMessageProcessor implements IMessageProcessor {
 	 * @param processors the {@link ObjectProcessor} to set
 	 * @since Envoy Server Standalone v0.1-alpha
 	 */
-	public ObjectMessageProcessor(Set<ObjectProcessor<?, ?>> processors) {
-		this.processors			= processors;
-	}
+	public ObjectMessageProcessor(Set<ObjectProcessor<?>> processors) { this.processors = processors; }
 
 	@SuppressWarnings("unchecked")
 	@Override
@@ -45,25 +41,17 @@ public class ObjectMessageProcessor implements IMessageProcessor {
 			System.out.println("Read object: " + obj.toString());
 
 			// Process object
-			processors.stream().filter(p -> p.getInputClass().isInstance(obj)).forEach((@SuppressWarnings("rawtypes") ObjectProcessor p) -> {
-				Object responseObj = p.process(p.getInputClass().cast(obj), message.socketId);
-				if (responseObj != null) {
-					// Create message targeted at the client
-					Message response = writeProxy.getMessage();
-					response.socketId = message.socketId;
-
-					// Serialize object to byte array
-					ByteArrayOutputStream baos = new ByteArrayOutputStream();
-					try (ObjectOutputStream oout = new ObjectOutputStream(baos)) {
-						oout.writeObject(responseObj);
+			processors.stream()
+				.filter(p -> p.getInputClass().isInstance(obj))
+				.forEach((@SuppressWarnings(
+					"rawtypes"
+				) ObjectProcessor p) -> {
+					try {
+						p.process(p.getInputClass().cast(obj), message.socketId, new ObjectWriteProxy(writeProxy));
 					} catch (IOException e) {
 						e.printStackTrace();
 					}
-					byte[] objBytes = baos.toByteArray();
-					response.writeToMessage(objBytes);
-					writeProxy.enqueue(response);
-				}
-			});
+				});
 		} catch (IOException | ClassNotFoundException e) {
 			e.printStackTrace();
 		}
diff --git a/src/main/java/envoy/server/net/ObjectWriteProxy.java b/src/main/java/envoy/server/net/ObjectWriteProxy.java
new file mode 100644
index 0000000..b1dc337
--- /dev/null
+++ b/src/main/java/envoy/server/net/ObjectWriteProxy.java
@@ -0,0 +1,34 @@
+package envoy.server.net;
+
+import java.io.IOException;
+
+import com.jenkov.nioserver.Message;
+import com.jenkov.nioserver.WriteProxy;
+
+import envoy.util.SerializationUtils;
+
+/**
+ * Project: <strong>envoy-server-standalone</strong><br>
+ * File: <strong>ObjectWriteProxy.java</strong><br>
+ * Created: <strong>04.01.2020</strong><br>
+ * 
+ * @author Kai S. K. Engelbart
+ * @since Envoy Server Standalone v0.1-alpha
+ */
+public class ObjectWriteProxy {
+
+	private final WriteProxy writeProxy;
+
+	public ObjectWriteProxy(WriteProxy writeProxy) { this.writeProxy = writeProxy; }
+
+	public void write(long recipientSocketId, Object obj) throws IOException {
+		// Create message targeted at the client
+		Message response = writeProxy.getMessage();
+		response.socketId = recipientSocketId;
+
+		// Serialize object to byte array
+		byte[] objBytes = SerializationUtils.writeToByteArray(obj);
+		response.writeToMessage(objBytes);
+		writeProxy.enqueue(response);
+	}
+}
diff --git a/src/main/resources/META-INF/persistence.xml b/src/main/resources/META-INF/persistence.xml
new file mode 100644
index 0000000..4d937c9
--- /dev/null
+++ b/src/main/resources/META-INF/persistence.xml
@@ -0,0 +1,29 @@
+<persistence xmlns="http://xmlns.jcp.org/xml/ns/persistence"
+	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+	xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence
+             http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd"
+	version="2.1">
+
+	<persistence-unit name="envoy"
+		transaction-type="RESOURCE_LOCAL">
+
+		<properties>
+			<property name="javax.persistence.jdbc.driver"
+				value="org.postgresql.Driver" /> <!-- DB Driver -->
+			<property name="javax.persistence.jdbc.url"
+				value="jdbc:postgresql://localhost/envoy" /> <!-- BD Mane -->
+			<property name="javax.persistence.jdbc.user" value="envoy" /> <!-- DB User -->
+			<property name="javax.persistence.jdbc.password"
+				value="envoy" /> <!-- DB Password -->
+
+			<property name="hibernate.dialect"
+				value="org.hibernate.dialect.PostgreSQL95Dialect" /> <!-- DB Dialect -->
+			<property name="hibernate.hbm2ddl.auto" value="update" /> <!-- create / create-drop / update -->
+
+			<property name="hibernate.show_sql" value="true" /> <!-- Show SQL in console -->
+			<property name="hibernate.format_sql" value="true" /> <!-- Show SQL formatted -->
+		</properties>
+
+	</persistence-unit>
+
+</persistence>
\ No newline at end of file