MailMessage mailObj = new MailMessage();
      
      mailObj.From = new MailAddress("mayun@qq.com"); //发送人邮箱地址   
      mailObj.To.Add("mahuateng@qq.com");  //收件人邮箱地址
      mailObj.Subject = "账户激活";  //主题
      mailObj.Body = mailbody;  //正文,
      mailObj.IsBodyHtml = true; //表示正文内容是HTML

      SmtpClient smtp = new SmtpClient();
      smtp.Host = "smtp.sina.cn";     //smtp服务器名称
      smtp.UseDefaultCredentials = true;
      smtp.Credentials = new NetworkCredential("mayun@qq.com", "pwd"); //发送人的登录名和密码
      smtp.Send(mailObj);