try
            {
                //準備郵件內容
                MailMessage message = new MailMessage                  ("abc@163.com", "abc@163.com", "測試郵件發送", "查看附件 ");
                message.Attachments.Add(new Attachment(@"D:/a.txt"));
                message.PRiority = MailPriority.High;
                message.IsBodyHtml = false;

                 //準備安全憑證
                   NetworkCredential nc= new NetworkCredential("abc","郵箱密碼");

                 //準備SMTP,發送電子郵件
                   SmtpClient client = new SmtpClient("smtp.163.com",25);
                client.DeliveryMethod = SmtpDeliveryMethod.Network;
                client.Credentials = nc;
                client.Send(message);
                MessageBox.Show("郵件發送成功!!");
            }
            catch (FormatException ex)
            {
                MessageBox.Show(ex.Message);
            }
            catch (SmtpException ex)
            {
                MessageBox.Show(ex.Message);
            }