SMTP 服务器要求安全连接或客户端未通过身份验证。

   protected void Cmd_Reg_Click(object sender, EventArgs e)
        {
              Random random = new Random();
                    string checkCode = "";
                    for (int i = 0; i <= 4; i++)
                    {
                        int num = random.Next(1, 10);
                        checkCode += num.ToString();
                    }
                    string validataCode = FormsAuthentication.HashPasswordForStoringInConfigFile(checkCode, "md5");
             SqlConnection conn = new SqlConnection(str);
            conn.Open();
            string sql = "insert into Email(UserId,UserPas,mail,AddDate,ValidataCode,UserState) values(@UserId,@UserPas,@mail,@AddDate,@ValidataCode,@UserState)";
            SqlCommand cmd = new SqlCommand(sql,conn);
            SqlParameter[] param = { 
                                   new SqlParameter("@UserId",Txt_Name.Text),
                                   new  SqlParameter("@UserPas",Txt_Pwd.Text),
                                   new  SqlParameter("@mail",Txt_Email.Text),
                                   new  SqlParameter("@AddDate",DateTime.Now),
                                   new  SqlParameter("@ValidataCode", validataCode),
                                    new  SqlParameter("@UserState",false),
                                   };
            cmd.Parameters.AddRange(param);
            int result =  cmd.ExecuteNonQuery();
            conn.Close();
            if (result > 0)
            {
                ClientScript.RegisterStartupScript(this.Page.GetType(), "alert", "<script>alert('ok')</script>");
                string strSmtpServer = "smtp.gmail.com";
                string strFrom ="[email protected]";
                string strFromPass = "123456";
                string strto = Txt_Email.Text;
                string strSubject = "账号激活";
              StringBuilder strBody = new StringBuilder();
                strBody.Append("点击下面链接激活账号，48小时生效，否则就要重新注册账号，链接只能使用一次，请尽快激活！</br>");
                strBody.Append("<a href='http://localhost:2493/web/Operate.aspx?userName=" + Txt_Name.Text + "&validateCode=" + validataCode + "'>点击这里</a></br>");
                strBody.Append("如未能激活请点击下面链接：<a href='http://localhost:2493/web/Operate.aspx?userName=" + Txt_Name.Text + "&validateCode=" + validataCode + "'>http://localhost:2493/web/Operate.aspx?userName=" + Txt_Name.Text + "&validateCode=" + validataCode + "</a></br>");
                SendSMTPEMail(strSmtpServer, strFrom, strFromPass, strto, strSubject, strBody.ToString());
            }
            else
            {
                ClientScript.RegisterStartupScript(this.Page.GetType(), "alert", "<script>alert('Nok')</script>");
            }    
        }
        //发送邮件
        public void SendSMTPEMail(string strSmtpServer, string strFrom, string strFromPass, string strto, string strSubject, string strBody)
        {      
          MailMessage message = new MailMessage(strFrom, strto, strSubject, strBody);
            message.BodyEncoding = System.Text.Encoding.UTF8;
            message.IsBodyHtml = true;
            message.Priority = MailPriority.High;
           SmtpClient client = new SmtpClient(strSmtpServer);
            client.UseDefaultCredentials = true;
            client.Credentials =
            new  NetworkCredential(strFrom, strFromPass);
            client.DeliveryMethod = SmtpDeliveryMethod.Network;
            client.EnableSsl = false;
            client.Send(message);
        }