第四部分，私有方法至结束

        /// <summary>
        /// SMTP回应代码哈希表
        /// </summary>
        private void SMTPCodeAdd()
        {
            ErrCodeHT.Add("500","邮箱地址错误");
            ErrCodeHT.Add("501","参数格式错误");
            ErrCodeHT.Add("502","命令不可实现");
            ErrCodeHT.Add("503","服务器需要SMTP验证");
            ErrCodeHT.Add("504","命令参数不可实现");
            ErrCodeHT.Add("421","服务未就绪，关闭传输信道");
            ErrCodeHT.Add("450","要求的邮件操作未完成，邮箱不可用（例如，邮箱忙）");
            ErrCodeHT.Add("550","要求的邮件操作未完成，邮箱不可用（例如，邮箱未找到，或不可访问）");
            ErrCodeHT.Add("451","放弃要求的操作；处理过程中出错");
            ErrCodeHT.Add("551","用户非本地，请尝试<forward-path>");
            ErrCodeHT.Add("452","系统存储不足，要求的操作未执行");
            ErrCodeHT.Add("552","过量的存储分配，要求的操作未执行");
            ErrCodeHT.Add("553","邮箱名不可用，要求的操作未执行（例如邮箱格式错误）");
            ErrCodeHT.Add("432","需要一个密码转换");
            ErrCodeHT.Add("534","认证机制过于简单");
            ErrCodeHT.Add("538","当前请求的认证机制需要加密");
            ErrCodeHT.Add("454","临时认证失败");
            ErrCodeHT.Add("530","需要认证");

            RightCodeHT.Add("220","服务就绪");
            RightCodeHT.Add("250","要求的邮件操作完成");
            RightCodeHT.Add("251","用户非本地，将转发向<forward-path>");
            RightCodeHT.Add("354","开始邮件输入，以<enter>.<enter>结束");
            RightCodeHT.Add("221","服务关闭传输信道");
            RightCodeHT.Add("334","服务器响应验证Base64字符串");
            RightCodeHT.Add("235","验证成功");
        }


        /// <summary>
        /// 将字符串编码为Base64字符串
        /// </summary>
        /// <param name="estr">要编码的字符串</param>
        private string Base64Encode(string str)
        {
            byte[] barray;
            barray=Encoding.Default.GetBytes(str);
            return Convert.ToBase64String(barray);
        }


        /// <summary>
        /// 将Base64字符串解码为普通字符串
        /// </summary>
        /// <param name="dstr">要解码的字符串</param>
        private string Base64Decode(string str)
        {
            byte[] barray;
            barray=Convert.FromBase64String(str);
            return Encoding.Default.GetString(barray);
        }

       
        /// <summary>
        /// 得到上传附件的文件流
        /// </summary>
        /// <param name="FilePath">附件的绝对路径</param>
        private string GetStream(string FilePath)
        {
            //建立文件流对象
            System.IO.FileStream FileStr=new System.IO.FileStream(FilePath,System.IO.FileMode.Open);
            byte[] by=new byte[System.Convert.ToInt32(FileStr.Length)];
            FileStr.Read(by,0,by.Length);
            FileStr.Close();
            return(System.Convert.ToBase64String(by));
        }


        /// <summary>
        /// 发送SMTP命令
        /// </summary>    
        private bool SendCommand(string str)
        {
            byte[]  WriteBuffer;
            if(str==nullstr.Trim()=="")
            {
                return true;
            }
            logs+=str;
            logs+=(enter+enter);
            htmllog+="<font color=''blue''>";
            htmllog+=str;
            htmllog+="</font></br>";
            WriteBuffer = Encoding.Default.GetBytes(str);
            try
            {
                ns.Write(WriteBuffer,0,WriteBuffer.Length);
            }
            catch
            {
                errmsg="网络连接错误";
                return false;
            }
            return true;
        }

        /// <summary>
        /// 接收SMTP服务器回应
        /// </summary>
        private string RecvResponse()
        {
            int StreamSize;
            string ReturnValue = "";
            byte[]  ReadBuffer = new byte[1024] ;
            try
            {
                StreamSize=ns.Read(ReadBuffer,0,ReadBuffer.Length);
            }
            catch
            {
                errmsg="网络连接错误";
                return "false";
            }

            if (StreamSize==0)
            {
                return ReturnValue ;
            }
            else
            {
                ReturnValue = Encoding.Default.GetString(ReadBuffer).Substring(0,StreamSize);
                logs+=ReturnValue + enter + enter;
                htmllog+="<font color=''#990000''>";
                htmllog+=ReturnValue;
                htmllog+="</font></br>";
                return  ReturnValue;
            }
        }


        /// <summary>
        /// 与服务器交互，发送一条命令并接收回应。
        /// </summary>
        /// <param name="Command">一个要发送的命令</param>
        /// <param name="errstr">如果错误，要反馈的信息</param>
        private bool Dialog(string str,string errstr)
        {
            if(str==nullstr.Trim()=="")
            {
                return true;
            }
            if(SendCommand(str))
            {
                string RR=RecvResponse();
                if(RR=="false")
                {
                    return false;
                }
                string RRCode=RR.Substring(0,3);
                if(RightCodeHT[RRCode]!=null)
                {
                    return true;
                }
                else
                {
                    if(ErrCodeHT[RRCode]!=null)
                    {
                        errmsg+=(RRCode+ErrCodeHT[RRCode].ToString());
                        errmsg+=enter;
                    }
                    else
                    {
                        errmsg+=RR;
                    }
                    errmsg+=errstr;
                    return false;
                }
            }
            else
            {
                return false;
            }

        }


        /// <summary>
        /// 与服务器交互，发送一组命令并接收回应。
        /// </summary>

        private bool Dialog(string[] str,string errstr)
        {
            for(int i=0;i<str.Length;i++)
            {
                if(!Dialog(str[i],""))
                {
                    errmsg+=enter;
                    errmsg+=errstr;
                    return false;
                }
            }

            return true;
        }


        //发送邮件
        private bool SendEmail()
        {
            //连接网络
            try
            {
                tc=new TcpClient(mailserver,mailserverport);
            }
            catch(Exception e)
            {
                errmsg=e.ToString();
                return false;
            }

            ns = tc.GetStream();
            SMTPCodeAdd();

            //验证网络连接是否正确
            if(RightCodeHT[RecvResponse().Substring(0,3)]==null)
            {
                errmsg="网络连接失败";
                return false;
            }


            string[] SendBuffer;
            string SendBufferstr;

            //进行SMTP验证
            if(ESmtp)
            {
                SendBuffer=new String[4];
                SendBuffer[0]="EHLO " + mailserver + enter;
                SendBuffer[1]="AUTH LOGIN" + enter;
                SendBuffer[2]=Base64Encode(username) + enter;
                SendBuffer[3]=Base64Encode(password) + enter;
                if(!Dialog(SendBuffer,"SMTP服务器验证失败，请核对用户名和密码。"))
                    return false;
            }
            else
            {
                SendBufferstr="HELO " + mailserver + enter;
                if(!Dialog(SendBufferstr,""))
                    return false;
            }

            //
            SendBufferstr="MAIL FROM:<" + From + ">" + enter;
            if(!Dialog(SendBufferstr,"发件人地址错误，或不能为空"))
                return false;

            //
            SendBuffer=new string[recipientmaxnum];
            for(int i=0;i<Recipient.Count;i++)
            {

                SendBuffer[i]="RCPT TO:<" + Recipient[i].ToString() +">" + enter;

            }
            if(!Dialog(SendBuffer,"收件人地址有误"))
                return false;

            SendBufferstr="DATA" + enter;
            if(!Dialog(SendBufferstr,""))
                return false;

            SendBufferstr="From:" + FromName + "<" + From +">" +enter;

            SendBufferstr += "To:=?"+Charset.ToUpper()+"?B?"+Base64Encode(RecipientName)+"?="+"<"+Recipient[0]+">"+enter;
            SendBufferstr+="CC:";
            for(int i=0;i<Recipient.Count;i++)
            {
                SendBufferstr+=Recipient[i].ToString() + "<" + Recipient[i].ToString() +">,";
            }
            SendBufferstr+=enter;


            if(Charset=="")
            {
                SendBufferstr+="Subject:" + Subject + enter;
            }
            else
            {
                SendBufferstr+="Subject:" + "=?" + Charset.ToUpper() + "?B?" + Base64Encode(Subject) +"?=" +enter;
            }

            SendBufferstr+="X-Priority:" + priority + enter;
            SendBufferstr+="X-MSMail-Priority:" + priority + enter;
            SendBufferstr+="Importance:" + priority + enter;
            SendBufferstr+="X-Mailer: Huolx.Pubclass" + enter;
            SendBufferstr+="MIME-Version: 1.0" + enter;

            SendBufferstr += "Content-Type: multipart/mixed;"+enter;//内容格式和分隔符
            SendBufferstr += "   boundary=\"----=_NextPart_000_00D6_01C29593.AAB31770\""+enter;
            SendBufferstr += "------=_NextPart_000_00D6_01C29593.AAB31770"+enter;

            if(Html)
            {
                SendBufferstr+="Content-Type: text/html;" + enter;
            }
            else
            {
                SendBufferstr+="Content-Type: text/plain;" + enter;
            }

            if(Charset=="")
            {
                SendBufferstr+="   charset=\"iso-8859-1\"" + enter;
            }
            else
            {
                SendBufferstr+="   charset=\"" + Charset.ToLower() + "\"" + enter;
            }
            //SendBufferstr += "Content-Transfer-Encoding: base64"+enter;

            SendBufferstr+="Content-Transfer-Encoding: base64" + enter + enter;

            SendBufferstr+= Base64Encode(Body) + enter;
            if(Attachments.Count!=0)
            {
                foreach(string filepath in Attachments)
                {
                
                    SendBufferstr += "------=_NextPart_000_00D6_01C29593.AAB31770"+enter;
                    SendBufferstr += "Content-Type: application/octet-stream"+enter;
                    SendBufferstr += "   name=\"=?"+Charset.ToUpper()+"?B?"+Base64Encode(filepath.Substring(filepath.LastIndexOf("\\")+1))+"?=\""+enter;
                    SendBufferstr += "Content-Transfer-Encoding: base64"+enter;
                    SendBufferstr += "Content-Disposition: attachment;"+enter;
                    SendBufferstr += "   filename=\"=?"+Charset.ToUpper()+"?B?"+Base64Encode(filepath.Substring(filepath.LastIndexOf("\\")+1))+"?=\""+enter+enter;
                    SendBufferstr += GetStream(filepath)+enter+enter;
                }
            }
            SendBufferstr += "------=_NextPart_000_00D6_01C29593.AAB31770--"+enter+enter;
          
          
            SendBufferstr += enter + "." + enter;

            if(!Dialog(SendBufferstr,"错误信件信息"))
                return false;


            SendBufferstr="QUIT" + enter;
            if(!Dialog(SendBufferstr,"断开连接时错误"))
                return false;


            ns.Close();
            tc.Close();
            return true;
        }

               
    }

}