예제 #1
0
        /// <summary>
        /// Relay data read from one connection to another.
        /// </summary>
        /// <param name="o">A TransmitArguments object containing local and remote server parameters.</param>
        private async void RelayData(object o)
        {
            // Cast the passed-in parameters back to their original objects.
            TransmitArguments arguments          = (TransmitArguments)o;
            Stream            clientStream       = arguments.ClientStream;
            Stream            remoteServerStream = arguments.RemoteServerStream;

            // A byte array to streamline bit shuffling.
            char[] buffer = new char[Constants.SMALLBUFFERSIZE];

            // Placeholder variables to track the current message being transmitted.
            StringBuilder messageBuilder = new StringBuilder(Constants.SMALLSBSIZE);

            // The overall number of bytes transmitted on this connection.
            ulong bytesTransmitted = 0;

            if (arguments.Credential != null)
            {
                UserName = arguments.Credential.UserName;
            }

            bool stillReceiving = true;

            try
            {
                using (StreamReader clientStreamReader = new StreamReader(clientStream))
                {
                    using (StreamWriter remoteServerStreamWriter = new StreamWriter(remoteServerStream))
                    {
                        remoteServerStreamWriter.AutoFlush = true;

                        while (Started && stillReceiving)
                        {
                            // Read data from the source and send it to its destination.
                            string stringRead = await clientStreamReader.ReadLineAsync();

                            if (stringRead != null)
                            {
                                int bytesRead = stringRead.Length;
                                bytesTransmitted += (ulong)bytesRead;

                                messageBuilder.AppendLine(stringRead);

                                // If this data comes from the client, log it.  Otherwise, process it.
                                if (arguments.IsClient)
                                {
                                    bool messageRelayed = false;

                                    string[] commandParts = stringRead.Substring(0, stringRead.Length).Split(new char[] { ' ' }, 2);

                                    // Optionally replace credentials with those from our settings file.
                                    if (commandParts.Length == 2)
                                    {
                                        if (commandParts[0] == "USER")
                                        {
                                            if (arguments.Credential != null)
                                            {
                                                await remoteServerStreamWriter.WriteLineAsync("USER " + arguments.Credential.UserName);

                                                ProxyFunctions.Log(LogWriter, SessionId, arguments.ConnectionId.ToString(), "C: USER " + arguments.Credential.UserName, Proxy.LogLevel.Raw, LogLevel);

                                                messageRelayed = true;
                                            }
                                            else
                                            {
                                                UserName = commandParts[1];
                                            }
                                        }
                                        else if (arguments.Credential != null && commandParts[0] == "PASS")
                                        {
                                            await remoteServerStreamWriter.WriteLineAsync("PASS" + arguments.Credential.Password);

                                            ProxyFunctions.Log(LogWriter, SessionId, arguments.ConnectionId.ToString(), "C: PASS " + arguments.Credential.Password, Proxy.LogLevel.Raw, LogLevel);

                                            messageRelayed = true;
                                        }
                                    }

                                    if (LogLevel == Proxy.LogLevel.Verbose)
                                    {
                                        ProxyFunctions.Log(LogWriter, SessionId, arguments.ConnectionId.ToString(), "Command {" + commandParts[0] + "} processed.", Proxy.LogLevel.Verbose, LogLevel);
                                    }

                                    if (!messageRelayed)
                                    {
                                        await remoteServerStreamWriter.WriteLineAsync(stringRead);

                                        ProxyFunctions.Log(LogWriter, SessionId, arguments.ConnectionId.ToString(), "C: " + stringRead, Proxy.LogLevel.Raw, LogLevel);
                                    }
                                }
                                else
                                {
                                    await remoteServerStreamWriter.WriteLineAsync(stringRead);

                                    ProxyFunctions.Log(LogWriter, SessionId, arguments.ConnectionId.ToString(), "S: " + stringRead, Proxy.LogLevel.Raw, LogLevel);

                                    // If we see a period between two linebreaks, treat it as the end of a message.
                                    if (stringRead == ".")
                                    {
                                        string message = messageBuilder.ToString();
                                        int    endPos  = message.IndexOf("\r\n.\r\n");

                                        if (message.Contains("\r\n\r\n"))
                                        {
                                            int lastOkPos = message.LastIndexOf("+OK", endPos);
                                            if (lastOkPos > -1)
                                            {
                                                message = message.Substring(message.IndexOf("\r\n", lastOkPos) + 2);
                                                if (message.IndexOf("application/x-pkcs7-signature") > -1 || message.IndexOf("application/pkcs7-mime") > -1 || !string.IsNullOrEmpty(arguments.ExportDirectory))
                                                {
                                                    Thread processThread = new Thread(new ParameterizedThreadStart(ProcessMessage));
                                                    processThread.Name = "OpaqueMail POP3 Proxy Signature Processor";
                                                    ProcessMessageArguments processMessageArguments = new ProcessMessageArguments();
                                                    processMessageArguments.MessageText     = message.Substring(0, message.Length - 5);
                                                    processMessageArguments.ConnectionId    = ConnectionId.ToString();
                                                    processMessageArguments.ExportDirectory = arguments.ExportDirectory;
                                                    processMessageArguments.InstanceId      = arguments.InstanceId;
                                                    processMessageArguments.DebugMode       = arguments.DebugMode;
                                                    processMessageArguments.UserName        = UserName;
                                                    processThread.Start(processMessageArguments);
                                                }
                                                messageBuilder.Remove(0, endPos + 5);
                                            }
                                        }

                                        messageBuilder.Clear();
                                    }
                                }
                            }
                            else
                            {
                                stillReceiving = false;
                            }
                        }
                    }
                }
            }
            catch (IOException)
            {
                // Ignore either stream being closed.
            }
            catch (ObjectDisposedException)
            {
                // Ignore either stream being closed.
            }
            catch (Exception ex)
            {
                // Log other exceptions.
                if (arguments.DebugMode || System.Diagnostics.Debugger.IsAttached)
                {
                    ProxyFunctions.Log(LogWriter, SessionId, arguments.ConnectionId, "Exception while transmitting data: " + ex.ToString(), Proxy.LogLevel.Error, LogLevel);
                }
                else
                {
                    ProxyFunctions.Log(LogWriter, SessionId, arguments.ConnectionId, "Exception while transmitting data: " + ex.Message, Proxy.LogLevel.Error, LogLevel);
                }
            }
            finally
            {
                // If sending to the local client, log the connection being closed.
                if (!arguments.IsClient)
                {
                    ProxyFunctions.Log(LogWriter, SessionId, arguments.ConnectionId, "Connection from {" + arguments.IPAddress + "} closed after transmitting {" + bytesTransmitted.ToString("N0") + "} bytes.", Proxy.LogLevel.Information, LogLevel);
                }

                if (clientStream != null)
                {
                    clientStream.Dispose();
                }
                if (remoteServerStream != null)
                {
                    remoteServerStream.Dispose();
                }
            }
        }
예제 #2
0
        /// <summary>
        /// Handle an incoming POP3 connection, from connection to completion.
        /// </summary>
        /// <param name="parameters">Pop3ProxyConnectionArguments object containing all parameters for this connection.</param>
        private void ProcessConnection(object parameters)
        {
            // Cast the passed-in parameters back to their original objects.
            Pop3ProxyConnectionArguments arguments = (Pop3ProxyConnectionArguments)parameters;

            try
            {
                TcpClient client       = arguments.TcpClient;
                Stream    clientStream = client.GetStream();

                // Capture the client's IP information.
                PropertyInfo pi = clientStream.GetType().GetProperty("Socket", BindingFlags.NonPublic | BindingFlags.Instance);
                string       ip = ((Socket)pi.GetValue(clientStream, null)).RemoteEndPoint.ToString();
                if (ip.IndexOf(":") > -1)
                {
                    ip = ip.Substring(0, ip.IndexOf(":"));
                }

                // If the IP address range filter contains the localhost entry 0.0.0.0, check if the client IP is a local address and update it to 0.0.0.0 if so.
                if (arguments.AcceptedIPs.IndexOf("0.0.0.0") > -1)
                {
                    if (ip == "127.0.0.1")
                    {
                        ip = "0.0.0.0";
                    }
                    else
                    {
                        IPHostEntry hostEntry = Dns.GetHostEntry(Dns.GetHostName());
                        foreach (IPAddress hostIP in hostEntry.AddressList)
                        {
                            if (hostIP.ToString() == ip)
                            {
                                ip = "0.0.0.0";
                                break;
                            }
                        }
                    }
                }

                // Validate that the IP address is within an accepted range.
                if (!ProxyFunctions.ValidateIP(arguments.AcceptedIPs, ip))
                {
                    ProxyFunctions.Log(LogWriter, SessionId, arguments.ConnectionId, "Connection rejected from {" + ip + "} due to its IP address.", Proxy.LogLevel.Warning, LogLevel);

                    Functions.SendStreamString(clientStream, new byte[Constants.SMALLBUFFERSIZE], "500 IP address [" + ip + "] rejected.\r\n");

                    if (clientStream != null)
                    {
                        clientStream.Dispose();
                    }
                    if (client != null)
                    {
                        client.Close();
                    }

                    return;
                }

                ProxyFunctions.Log(LogWriter, SessionId, arguments.ConnectionId, "New connection established from {" + ip + "}.", Proxy.LogLevel.Information, LogLevel);

                // If supported, upgrade the session's security through a TLS handshake.
                if (arguments.LocalEnableSsl)
                {
                    ProxyFunctions.Log(LogWriter, SessionId, arguments.ConnectionId, "Starting local TLS/SSL protection for {" + ip + "}.", Proxy.LogLevel.Information, LogLevel);
                    clientStream = new SslStream(clientStream);
                    ((SslStream)clientStream).AuthenticateAsServer(arguments.Certificate);
                }

                // Connect to the remote server.
                TcpClient remoteServerClient = new TcpClient(arguments.RemoteServerHostName, arguments.RemoteServerPort);
                Stream    remoteServerStream = remoteServerClient.GetStream();

                // If supported, upgrade the session's security through a TLS handshake.
                if (arguments.RemoteServerEnableSsl)
                {
                    ProxyFunctions.Log(LogWriter, SessionId, arguments.ConnectionId, "Starting remote TLS/SSL protection with {" + arguments.RemoteServerHostName + "}.", Proxy.LogLevel.Information, LogLevel);
                    remoteServerStream = new SslStream(remoteServerStream);
                    ((SslStream)remoteServerStream).AuthenticateAsClient(arguments.RemoteServerHostName);
                }

                // Relay server data to the client.
                TransmitArguments remoteServerToClientArguments = new TransmitArguments();
                remoteServerToClientArguments.ClientStream       = remoteServerStream;
                remoteServerToClientArguments.RemoteServerStream = clientStream;
                remoteServerToClientArguments.IsClient           = false;
                remoteServerToClientArguments.ConnectionId       = ConnectionId.ToString();
                remoteServerToClientArguments.InstanceId         = arguments.InstanceId;
                remoteServerToClientArguments.DebugMode          = arguments.DebugMode;
                remoteServerToClientArguments.IPAddress          = ip;
                remoteServerToClientArguments.ExportDirectory    = arguments.ExportDirectory;
                Thread remoteServerToClientThread = new Thread(new ParameterizedThreadStart(RelayData));
                remoteServerToClientThread.Name = "OpaqueMail POP3 Proxy Server to Client";
                remoteServerToClientThread.Start(remoteServerToClientArguments);

                // Relay client data to the remote server.
                TransmitArguments clientToRemoteServerArguments = new TransmitArguments();
                clientToRemoteServerArguments.ClientStream       = clientStream;
                clientToRemoteServerArguments.RemoteServerStream = remoteServerStream;
                clientToRemoteServerArguments.IsClient           = true;
                clientToRemoteServerArguments.ConnectionId       = ConnectionId.ToString();
                clientToRemoteServerArguments.InstanceId         = arguments.InstanceId;
                clientToRemoteServerArguments.DebugMode          = arguments.DebugMode;
                clientToRemoteServerArguments.IPAddress          = ip;
                clientToRemoteServerArguments.Credential         = arguments.RemoteServerCredential;
                Thread clientToRemoteServerThread = new Thread(new ParameterizedThreadStart(RelayData));
                clientToRemoteServerThread.Name = "OpaqueMail POP3 Proxy Client to Server";
                clientToRemoteServerThread.Start(clientToRemoteServerArguments);
            }
            catch (SocketException ex)
            {
                if (arguments.DebugMode || System.Diagnostics.Debugger.IsAttached)
                {
                    ProxyFunctions.Log(LogWriter, SessionId, "Exception communicating with {" + arguments.RemoteServerHostName + "} on port {" + arguments.RemoteServerPort + "}: " + ex.ToString(), Proxy.LogLevel.Error, LogLevel);
                }
                else
                {
                    ProxyFunctions.Log(LogWriter, SessionId, "Exception communicating with {" + arguments.RemoteServerHostName + "} on port {" + arguments.RemoteServerPort + "}: " + ex.Message, Proxy.LogLevel.Error, LogLevel);
                }
            }
            catch (Exception ex)
            {
                if (arguments.DebugMode || System.Diagnostics.Debugger.IsAttached)
                {
                    ProxyFunctions.Log(LogWriter, SessionId, "Exception: " + ex.ToString(), Proxy.LogLevel.Error, LogLevel);
                }
                else
                {
                    ProxyFunctions.Log(LogWriter, SessionId, "Exception: " + ex.Message, Proxy.LogLevel.Error, LogLevel);
                }
            }
        }
예제 #3
0
        /// <summary>
        /// Relay data read from one connection to another.
        /// </summary>
        /// <param name="o">A TransmitArguments object containing local and remote server parameters.</param>
        private async void RelayData(object o)
        {
            // Cast the passed-in parameters back to their original objects.
            TransmitArguments arguments          = (TransmitArguments)o;
            Stream            clientStream       = arguments.ClientStream;
            Stream            remoteServerStream = arguments.RemoteServerStream;

            // A byte array to streamline bit shuffling.
            char[] buffer = new char[Constants.SMALLBUFFERSIZE];

            // Placeholder variables to track the current message being transmitted.
            bool          inMessage      = false;
            int           messageLength  = 0;
            StringBuilder messageBuilder = new StringBuilder(Constants.SMALLSBSIZE);

            // The overall number of bytes transmitted on this connection.
            ulong bytesTransmitted = 0;

            //  When a "[THROTTLED]" notice was last received.
            DateTime lastThrottleTime = new DateTime(1900, 1, 1);

            if (arguments.Credential != null)
            {
                UserName = arguments.Credential.UserName;
            }

            bool stillReceiving = true;

            try
            {
                using (StreamReader clientStreamReader = new StreamReader(clientStream))
                {
                    using (StreamWriter remoteServerStreamWriter = new StreamWriter(remoteServerStream))
                    {
                        remoteServerStreamWriter.AutoFlush = true;

                        while (Started && stillReceiving)
                        {
                            // Read data from the source and send it to its destination.
                            string stringRead = await clientStreamReader.ReadLineAsync();

                            if (stringRead != null)
                            {
                                int bytesRead = stringRead.Length;
                                bytesTransmitted += (ulong)bytesRead;

                                // If this data comes from the client, log it.  Otherwise, process it.
                                if (arguments.IsClient)
                                {
                                    bool messageRelayed = false;

                                    string[] commandParts = stringRead.Split(new char[] { ' ' }, 4);
                                    if (commandParts.Length > 1)
                                    {
                                        // Optionally, transform the login details.
                                        if (commandParts[1] == "LOGIN" && commandParts.Length == 4)
                                        {
                                            messageRelayed = TransformLogin(remoteServerStreamWriter, stringRead, arguments, ref UserName);
                                        }
                                        else
                                        {
                                            ProxyFunctions.Log(LogWriter, SessionId, arguments.ConnectionId.ToString(), "C: " + stringRead, Proxy.LogLevel.Raw, LogLevel);
                                        }

                                        // Remember the previous command.
                                        if (commandParts[1].ToUpper() == "UID" && commandParts.Length > 2)
                                        {
                                            LastCommandReceived = (commandParts[1] + " " + commandParts[2]).ToUpper();
                                        }
                                        else
                                        {
                                            LastCommandReceived = commandParts[1].ToUpper();
                                        }

                                        // Stop after a logout order is received.
                                        if (LastCommandReceived == "LOGOUT")
                                        {
                                            stillReceiving = false;
                                        }

                                        if (LogLevel == Proxy.LogLevel.Verbose)
                                        {
                                            switch (LastCommandReceived)
                                            {
                                            case "APPEND":
                                            case "AUTHENTICATE":
                                            case "CAPABILITY":
                                            case "CHECK":
                                            case "CLOSE":
                                            case "COPY":
                                            case "CREATE":
                                            case "DELETE":
                                            case "ENABLE":
                                            case "EXAMINE":
                                            case "EXPUNGE":
                                            case "FETCH":
                                            case "GETQUOTA":
                                            case "GETQUOTAROOT":
                                            case "LIST":
                                            case "LOGIN":
                                            case "LOGOUT":
                                            case "LSUB":
                                            case "MOVE":
                                            case "NOOP":
                                            case "NOTIFY":
                                            case "RENAME":
                                            case "SEARCH":
                                            case "SELECT":
                                            case "SETQUOTA":
                                            case "STATUS":
                                            case "STORE":
                                            case "SUBSCRIBE":
                                            case "UID COPY":
                                            case "UID FETCH":
                                            case "UID SEARCH":
                                            case "UID STORE":
                                            case "UNSUBSCRIBE":
                                            case "XLIST":
                                                ProxyFunctions.Log(LogWriter, SessionId, arguments.ConnectionId.ToString(), "Command {" + LastCommandReceived + "} processed.", Proxy.LogLevel.Verbose, LogLevel);
                                                break;
                                            }
                                        }
                                    }

                                    // If the command wasn't processed, send the raw command.
                                    if (!messageRelayed)
                                    {
                                        await remoteServerStreamWriter.WriteLineAsync(stringRead);
                                    }
                                }
                                else
                                {
                                    // If we're currently receiving a message, check to see if it's completed.
                                    if (inMessage)
                                    {
                                        messageBuilder.AppendLine(stringRead);
                                        if (messageBuilder.Length >= messageLength)
                                        {
                                            // If the message has been completed and it contains a signature, process it.
                                            string message = messageBuilder.ToString(0, messageLength);
                                            if (message.IndexOf("application/x-pkcs7-signature") > -1 || message.IndexOf("application/pkcs7-mime") > -1 || !string.IsNullOrEmpty(arguments.ExportDirectory))
                                            {
                                                Thread processThread = new Thread(new ParameterizedThreadStart(ProcessMessage));
                                                processThread.Name = "OpaqueMail IMAP Proxy Signature Processor";
                                                ProcessMessageArguments processMessageArguments = new ProcessMessageArguments();
                                                processMessageArguments.MessageText     = message;
                                                processMessageArguments.ConnectionId    = ConnectionId.ToString();
                                                processMessageArguments.ExportDirectory = arguments.ExportDirectory;
                                                processMessageArguments.InstanceId      = arguments.InstanceId;
                                                processMessageArguments.DebugMode       = arguments.DebugMode;
                                                processMessageArguments.UserName        = UserName;
                                                processThread.Start(processMessageArguments);
                                            }

                                            // We're no longer receiving a message, so continue.
                                            inMessage = false;
                                            messageBuilder.Clear();
                                        }
                                    }
                                    else
                                    {
                                        // Disallow proxy stream compression.
                                        if (stringRead.StartsWith("* CAPABILITY"))
                                        {
                                            stringRead = stringRead.Replace(" COMPRESS=DEFLATE", "");
                                        }

                                        // Check for IMAP meta flags.
                                        string betweenBraces = Functions.ReturnBetween(stringRead, "[", "]");
                                        switch (betweenBraces)
                                        {
                                        case "CLIENTBUG":
                                        case "CORRUPTION":
                                        case "OVERQUOTA":
                                        case "SERVERBUG":
                                        case "UNAVAILABLE":
                                            ProxyFunctions.Log(LogWriter, SessionId, ConnectionId.ToString(), stringRead.Substring(stringRead.IndexOf("[")), Proxy.LogLevel.Warning, LogLevel);
                                            break;

                                        case "THROTTLED":
                                            if (DateTime.Now - lastThrottleTime >= new TimeSpan(0, 20, 0))
                                            {
                                                ProxyFunctions.Log(LogWriter, SessionId, ConnectionId.ToString(), "Connection speed throttled by the remote server.", Proxy.LogLevel.Warning, LogLevel);
                                                lastThrottleTime = DateTime.Now;
                                            }
                                            break;
                                        }

                                        // Messages are denoted by FETCH headers with their lengths in curly braces.
                                        if (stringRead.ToUpper().Contains(" FETCH "))
                                        {
                                            int openBrace = stringRead.IndexOf("{");
                                            if (openBrace > -1)
                                            {
                                                int closeBrace = stringRead.IndexOf("}", openBrace);
                                                if (closeBrace > -1)
                                                {
                                                    // Only proceed if we can parse the size of the message.
                                                    if (int.TryParse(stringRead.Substring(openBrace + 1, closeBrace - openBrace - 1), out messageLength))
                                                    {
                                                        inMessage = true;
                                                    }
                                                }
                                            }
                                        }
                                    }

                                    await remoteServerStreamWriter.WriteLineAsync(stringRead);

                                    ProxyFunctions.Log(LogWriter, SessionId, arguments.ConnectionId.ToString(), "S: " + stringRead, Proxy.LogLevel.Raw, LogLevel);
                                }
                            }
                            else
                            {
                                stillReceiving = false;
                            }
                        }
                    }
                }
            }
            catch (IOException)
            {
                // Ignore either stream being closed.
            }
            catch (ObjectDisposedException)
            {
                // Ignore either stream being closed.
            }
            catch (Exception ex)
            {
                // Log other exceptions.
                if (arguments.DebugMode || System.Diagnostics.Debugger.IsAttached)
                {
                    ProxyFunctions.Log(LogWriter, SessionId, arguments.ConnectionId, "Exception while transmitting data: " + ex.ToString(), Proxy.LogLevel.Error, LogLevel);
                }
                else
                {
                    ProxyFunctions.Log(LogWriter, SessionId, arguments.ConnectionId, "Exception while transmitting data: " + ex.Message, Proxy.LogLevel.Error, LogLevel);
                }
            }
            finally
            {
                // If sending to the local client, log the connection being closed.
                if (!arguments.IsClient)
                {
                    ProxyFunctions.Log(LogWriter, SessionId, arguments.ConnectionId, "Connection from {" + arguments.IPAddress + "} closed after transmitting {" + bytesTransmitted.ToString("N0") + "} bytes.", Proxy.LogLevel.Information, LogLevel);
                }

                if (clientStream != null)
                {
                    clientStream.Dispose();
                }
                if (remoteServerStream != null)
                {
                    remoteServerStream.Dispose();
                }
            }
        }
예제 #4
0
        /// <summary>
        /// Optionally, replace credentials with those from our settings file.
        /// </summary>
        /// <param name="remoteServerStreamWriter">Remote stream writer to transform.</param>
        /// <param name="stringRead">Login string read from the client.</param>
        /// <param name="arguments">A TransmitArguments object containing local and remote server parameters.</param>
        /// <param name="Username">Username of the connected account.</param>
        /// <returns></returns>
        private bool TransformLogin(StreamWriter remoteServerStreamWriter, string stringRead, TransmitArguments arguments, ref string Username)
        {
            string[] commandParts = stringRead.Split(new char[] { ' ' }, 4);
            if (arguments.Credential != null)
            {
                remoteServerStreamWriter.WriteLine(commandParts[0] + " " + commandParts[1] + " " + arguments.Credential.UserName + " " + arguments.Credential.Password);

                ProxyFunctions.Log(LogWriter, SessionId, arguments.ConnectionId.ToString(), "C: " + commandParts[0] + " " + commandParts[1] + " " + arguments.Credential.UserName + " " + arguments.Credential.Password, Proxy.LogLevel.Raw, LogLevel);

                return(true);
            }
            else
            {
                UserName = commandParts[2].Replace("\"", "");
                return(false);
            }
        }
예제 #5
0
        /// <summary>
        /// Handle an incoming POP3 connection, from connection to completion.
        /// </summary>
        /// <param name="parameters">Pop3ProxyConnectionArguments object containing all parameters for this connection.</param>
        private void ProcessConnection(object parameters)
        {
            // Cast the passed-in parameters back to their original objects.
            Pop3ProxyConnectionArguments arguments = (Pop3ProxyConnectionArguments)parameters;

            try
            {
                TcpClient client = arguments.TcpClient;
                Stream clientStream = client.GetStream();

                // Capture the client's IP information.
                PropertyInfo pi = clientStream.GetType().GetProperty("Socket", BindingFlags.NonPublic | BindingFlags.Instance);
                string ip = ((Socket)pi.GetValue(clientStream, null)).RemoteEndPoint.ToString();
                if (ip.IndexOf(":") > -1)
                    ip = ip.Substring(0, ip.IndexOf(":"));

                // If the IP address range filter contains the localhost entry 0.0.0.0, check if the client IP is a local address and update it to 0.0.0.0 if so.
                if (arguments.AcceptedIPs.IndexOf("0.0.0.0") > -1)
                {
                    if (ip == "127.0.0.1")
                        ip = "0.0.0.0";
                    else
                    {
                        IPHostEntry hostEntry = Dns.GetHostEntry(Dns.GetHostName());
                        foreach (IPAddress hostIP in hostEntry.AddressList)
                        {
                            if (hostIP.ToString() == ip)
                            {
                                ip = "0.0.0.0";
                                break;
                            }
                        }
                    }
                }

                // Validate that the IP address is within an accepted range.
                if (!ProxyFunctions.ValidateIP(arguments.AcceptedIPs, ip))
                {
                    ProxyFunctions.Log(LogWriter, SessionId, arguments.ConnectionId, "Connection rejected from {" + ip + "} due to its IP address.", Proxy.LogLevel.Warning, LogLevel);

                    Functions.SendStreamString(clientStream, new byte[Constants.SMALLBUFFERSIZE], "500 IP address [" + ip + "] rejected.\r\n");

                    if (clientStream != null)
                        clientStream.Dispose();
                    if (client != null)
                        client.Close();

                    return;
                }

                ProxyFunctions.Log(LogWriter, SessionId, arguments.ConnectionId, "New connection established from {" + ip + "}.", Proxy.LogLevel.Information, LogLevel);

                // If supported, upgrade the session's security through a TLS handshake.
                if (arguments.LocalEnableSsl)
                {
                    ProxyFunctions.Log(LogWriter, SessionId, arguments.ConnectionId, "Starting local TLS/SSL protection for {" + ip + "}.", Proxy.LogLevel.Information, LogLevel);
                    clientStream = new SslStream(clientStream);
                    ((SslStream)clientStream).AuthenticateAsServer(arguments.Certificate);
                }

                // Connect to the remote server.
                TcpClient remoteServerClient = new TcpClient(arguments.RemoteServerHostName, arguments.RemoteServerPort);
                Stream remoteServerStream = remoteServerClient.GetStream();

                // If supported, upgrade the session's security through a TLS handshake.
                if (arguments.RemoteServerEnableSsl)
                {
                    ProxyFunctions.Log(LogWriter, SessionId, arguments.ConnectionId, "Starting remote TLS/SSL protection with {" + arguments.RemoteServerHostName + "}.", Proxy.LogLevel.Information, LogLevel);
                    remoteServerStream = new SslStream(remoteServerStream);
                    ((SslStream)remoteServerStream).AuthenticateAsClient(arguments.RemoteServerHostName);
                }

                // Relay server data to the client.
                TransmitArguments remoteServerToClientArguments = new TransmitArguments();
                remoteServerToClientArguments.ClientStream = remoteServerStream;
                remoteServerToClientArguments.RemoteServerStream = clientStream;
                remoteServerToClientArguments.IsClient = false;
                remoteServerToClientArguments.ConnectionId = ConnectionId.ToString();
                remoteServerToClientArguments.InstanceId = arguments.InstanceId;
                remoteServerToClientArguments.DebugMode = arguments.DebugMode;
                remoteServerToClientArguments.IPAddress = ip;
                remoteServerToClientArguments.ExportDirectory = arguments.ExportDirectory;
                Thread remoteServerToClientThread = new Thread(new ParameterizedThreadStart(RelayData));
                remoteServerToClientThread.Name = "OpaqueMail POP3 Proxy Server to Client";
                remoteServerToClientThread.Start(remoteServerToClientArguments);

                // Relay client data to the remote server.
                TransmitArguments clientToRemoteServerArguments = new TransmitArguments();
                clientToRemoteServerArguments.ClientStream = clientStream;
                clientToRemoteServerArguments.RemoteServerStream = remoteServerStream;
                clientToRemoteServerArguments.IsClient = true;
                clientToRemoteServerArguments.ConnectionId = ConnectionId.ToString();
                clientToRemoteServerArguments.InstanceId = arguments.InstanceId;
                clientToRemoteServerArguments.DebugMode = arguments.DebugMode;
                clientToRemoteServerArguments.IPAddress = ip;
                clientToRemoteServerArguments.Credential = arguments.RemoteServerCredential;
                Thread clientToRemoteServerThread = new Thread(new ParameterizedThreadStart(RelayData));
                clientToRemoteServerThread.Name = "OpaqueMail POP3 Proxy Client to Server";
                clientToRemoteServerThread.Start(clientToRemoteServerArguments);
            }
            catch (SocketException ex)
            {
                if (arguments.DebugMode || System.Diagnostics.Debugger.IsAttached)
                    ProxyFunctions.Log(LogWriter, SessionId, "Exception communicating with {" + arguments.RemoteServerHostName + "} on port {" + arguments.RemoteServerPort + "}: " + ex.ToString(), Proxy.LogLevel.Error, LogLevel);
                else
                    ProxyFunctions.Log(LogWriter, SessionId, "Exception communicating with {" + arguments.RemoteServerHostName + "} on port {" + arguments.RemoteServerPort + "}: " + ex.Message, Proxy.LogLevel.Error, LogLevel);
            }
            catch (Exception ex)
            {
                if (arguments.DebugMode || System.Diagnostics.Debugger.IsAttached)
                    ProxyFunctions.Log(LogWriter, SessionId, "Exception: " + ex.ToString(), Proxy.LogLevel.Error, LogLevel);
                else
                    ProxyFunctions.Log(LogWriter, SessionId, "Exception: " + ex.Message, Proxy.LogLevel.Error, LogLevel);
            }
        }