C# - email von einem POP Mail Server abholen

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Collections;
using System.Net.Sockets;
using System.Diagnostics;

namespace NetOffice_3
{
    public partial class Form12 : Form
    {
        public Form12()
        {
            InitializeComponent();
        }
 
// emails abholen -----------------------------------------------------------------------------

        private void F12B1_Click(object sender, EventArgs e)
        {
            try
            {
                string str1 = F12TSCmb2.Text;
                string str2 = F12TSCmb3.Text;
                string str3 = F12TSTB1.Text;

                POPServer svr = new POPServer();
                svr.Verbinden(str1, str2, str3);
                ArrayList list = svr.List();
                foreach (ServerMessage msg in list)
                {
                    ServerMessage smg2 = svr.Abholen(msg);
                    F12RTFBox1.AppendText("Nr." + smg2.number.ToString() + " ");
                    F12RTFBox1.AppendText(smg2.message.ToString() + "End\n\n");

                    svr.Entfernen(msg);
                }
                
                svr.Trennen();
            }
            catch (ServerException ex)
            {
                MessageBox.Show("Ein Fehler ist aufgetreten ..." + "Details: " + ex.ToString(), "NetOffice", MessageBoxButtons.OK, MessageBoxIcon.Warning);
                return;
            }
            catch (Exception ex)
            {
                MessageBox.Show("Ein Fehler ist aufgetreten ..." + "Details: " + ex.ToString(), "NetOffice", MessageBoxButtons.OK, MessageBoxIcon.Warning);
                return;             
            }

            MessageBox.Show("Keine weiteren Nachrichten vorhanden ...", "NetOffice", MessageBoxButtons.OK, MessageBoxIcon.Information);

        }

// Exceptionklasse definieren -----------------------------------------------------

        public class ServerException : System.ApplicationException
        {
            public ServerException(string str)
                : base(str)
            {
            }
        }

//---------------------------------------------------------------------------------
        public class ServerMessage
        {
            public long number;
            public long bytes;
            public bool retrieved;
            public string message;
        }

//---------------------------------------------------------------------------------
        public class POPServer : System.Net.Sockets.TcpClient
        {

//---------------------------------------------------------------------------------
            public void Verbinden(string server, string username, string password)
            {
                string message;
                string response;

                Connect(server, 110);
                response = Antwort();
                if (response.Substring(0, 3) != "+OK")
                {
                    throw new ServerException(response);
                }

                message = "USER " + username + "\r\n";
                Write(message);
                response = Antwort();
                if (response.Substring(0, 3) != "+OK")
                {
                    throw new ServerException(response);
                }

                message = "PASS " + password + "\r\n";
                Write(message);
                response = Antwort();
                if (response.Substring(0, 3) != "+OK")
                {
                    throw new ServerException(response);
                }
            }

// ------------------------------------------------------------------------------
            public void Trennen()
            {
                string message;
                string response;
                message = "QUIT\r\n";
                Write(message);
                response = Antwort();
                if (response.Substring(0, 3) != "+OK")
                {
                    throw new ServerException(response);
                }
            }

// ---------------------------------------------------------------------------------

            public ArrayList List()
            {
                string message;
                string response;

                ArrayList arl1 = new ArrayList();
                message = "LIST\r\n";
                Write(message);
                response = Antwort();
                if (response.Substring(0, 3) != "+OK")
                {
                    throw new ServerException(response);
                }

                while (true)
                {
                    response = Antwort();
                    if (response == ".\r\n")
                    {
                        return arl1;
                    }
                    else
                    {
                        ServerMessage smg = new ServerMessage();
                        char[] sps = { ' ' };
                        string[] values = response.Split(sps);
                        smg.number = Int32.Parse(values[0]);
                        smg.bytes = Int32.Parse(values[1]);
                        smg.retrieved = false;
                        arl1.Add(smg);
                        continue;
                    }
                }
            }

//Nachicht abholen -----------------------------------------------------------

            public ServerMessage Abholen(ServerMessage svm)
            {
                string message;
                string response;

                ServerMessage msg = new ServerMessage();
                msg.bytes = svm.bytes;
                msg.number = svm.number;

                message = "RETR " + svm.number + "\r\n";
                Write(message);
                response = Antwort();
                if (response.Substring(0, 3) != "+OK")
                {
                    throw new ServerException(response);
                }

                msg.retrieved = true;
                while (true)
                {
                    response = Antwort();
                    if (response == ".\r\n")
                    {
                        break;
                    }
                    else
                    {
                        msg.message += response;
                    }
                }

                return msg;
            }

// Nachrichten löschen ------------------------------------------------------

            public void Entfernen(ServerMessage svm)
            {
                string message;
                string response;

                message = "DELE " + svm.number + "\r\n";
                Write(message);
                response = Antwort();
                if (response.Substring(0, 3) != "+OK")
                {
                    throw new ServerException(response);
                }
            }

// Hilfsmethoden ------------------------------------------------------------

            private void Write(string message)
            {
                ASCIIEncoding enc = new ASCIIEncoding();

                byte[] WriteBuffer = new byte[2048]; 
                WriteBuffer = enc.GetBytes(message);

                NetworkStream stream = GetStream();
                stream.Write(WriteBuffer, 0, WriteBuffer.Length);                            
            }

// --------------------------------------------------------------------------

            private string Antwort()
            {
                ASCIIEncoding enc = new ASCIIEncoding();
                byte[] arr1 = new Byte[2048]; 
                NetworkStream stream = GetStream();
                int count = 0;
                while (true)
                {
                    byte[] arr2 = new Byte[2];
                    int bytes = stream.Read(arr2, 0, 1);
                    if (bytes == 1)
                    {
                        arr1[count] = arr2[0];
                        count++;

                        if (arr2[0] == '\n')
                        {
                            break;
                        }
                    }
                    else
                    {
                        break;
                    }
                }

                string arrl1 = enc.GetString(arr1, 0, count);
                return arrl1;
            }
        }

// Form12 End --------------------------------------------------------------------
    }
}