SmtpClient smtp = new SmtpClient(); //实例化一个SmtpClient
//可以支持SSL，
smtp.EnableSsl = useSsl;//smtp服务器是否启用SSL加密//可以支持SSL，
//可以支持 回复邮箱 ReplyTo
 MailMessage mm = new MailMessage(); //实例化一个邮件类
mm.ReplyTo = new MailAddress(replyToEmail, displayName,Encoding.Default);

 //准备发送
                SendCmd("MAIL FROM: <" + mail.MailFrom + ">\r\n");//必须加个‘<’、‘>’,否则出现500 bad Syntax 错误，即命令语法错误
                orderText += "MAIL FROM: <" + mail.MailFrom + ">\r\n";
                //if (GetStatusCode(ref orderText) != 250)
                //{ return false; }
                foreach (string to in mail.MailTo)
                {
                    SendCmd("RCPT TO: <" + to + ">\r\n");//必须加个‘<’、‘>’,否则出现500 bad Syntax 错误，即命令语法错误
                    orderText += "RCPT TO: <" + to + ">\r\n";
                    //if (GetStatusCode(ref orderText) != 250)
                    //{ return false; }
                }
                SendCmd("data\r\n");
                orderText += "data\r\n";
                //if (GetStatusCode(ref orderText) != 354)
                //{ return false; }
                StringBuilder content = new StringBuilder();

                //邮件头
                content.AppendFormat("From:{0}\r\n", mail.MailFrom);
                string toTxt = string.Empty;
                foreach (string to in mail.MailTo)
                {
                    toTxt += to + ";";
                }
                toTxt = toTxt.Substring(0, toTxt.Length - 1);
                content.AppendFormat("To:{0}\r\n", toTxt);//发送到达邮件
                content.AppendFormat("Date:{0}\r\n", mail.SendDate.ToString());//发送时间
                content.AppendFormat("Subject:{0}\r\n", mail.Subject);//邮件主题

                //邮件格式

                //邮件内容
                content.Append("\r\n");
                content.Append(mail.Body);//邮件内容
                content.Append("\r\n.\r\n");

                //邮件附件

                SendCmd(content.ToString());
                orderText += content.ToString();