主要是为了自己使用，大家可以自己去扩充。
全部代码：
using System;
using System.Text;
using System.IO;
using System.Net;
using System.Net.Sockets;

namespace OSLeagueForumXP.Components
{
    /// <summary>
    /// TcpClient派生类，用来进行SMTP服务器的连接工作
    /// </summary>
    public class SMTPClient : TcpClient
    {
        /// <summary>
        /// 进行SMTP服务器的连接
        /// </summary>
        public SMTPClient()
        {
        }
        /// <summary>
        /// 是否以连接
        /// </summary>
        /// <returns>连接为True，不连接为False</returns>
        public bool isConnected()
        {
            return Active;
        }
        
        /// <summary>
        /// 向服务器发送命令
        /// </summary>
        /// <param name="Command">命令</param>
        public void SendCommandToServer(string Command)
        {
            NetworkStream ns = this.GetStream() ;
            byte[]  WriteBuffer ;
            WriteBuffer = new byte[1024] ;
            WriteBuffer = Encoding.Default.GetBytes(Command);
            ns.Write(WriteBuffer,0,WriteBuffer.Length);
            return  ;
        }
        
        /// <summary>
        /// 取得服务器反馈信息
        /// </summary>
        /// <returns>字符串</returns>
        public string GetServerResponse()
        {
            int StreamSize ;
            string ReturnValue = "" ;
            byte[]  ReadBuffer ;
            NetworkStream ns = this.GetStream() ;
            ReadBuffer = new byte[1024] ;
            StreamSize =