如何通过C#在Windows应用程序中发送邮件

我的代码:

My code:

private void button1_Click(object sender, EventArgs e)
      {

          try
          {
              MailMessage mail = new MailMessage();
              mail.To.Add("shi01715@gmail.com");
              mail.To.Add(txtto.Text.ToString());
              mail.From = new MailAddress("shishir64092@gmail.com");
              mail.Subject = "School Name";
              string Body = txtmsg.Text;
              mail.IsBodyHtml = true;

              SmtpClient smtp = new SmtpClient("localhost", 25);
              smtp.Host = "smtp.gmail.com"; //Or Your SMTP Server Address
              smtp.Credentials = new System.Net.NetworkCredential
                   ("shishir64092@gmail.com", "rima001");
              smtp.DeliveryMethod = SmtpDeliveryMethod.Network;
              smtp.EnableSsl = true;
              smtp.Send(mail);
              MessageBox.Show("Mail Send");
          }
          catch (Exception ex)
          {
              MessageBox.Show(ex.Message);
          }
      }

我的App.Config:

My App.Config :

<?xml version="1.0" encoding="utf-8" ?>

<configuration>
  <system.net>
    <mailSettings>
      <smtp deliveryMethod="PickupDirectoryFromIis">
        <network defaultCredentials="true" host="localhost" port="25"/>
      </smtp>
    </mailSettings>
  </system.net>
</configuration>

错误:发送邮件失败

有人可以告诉我在Windows应用程序中发送邮件的问题在哪里吗?请帮助我.

Error: Failure sending mail

Can anybody tell me where is the problem for sending mail in windows application ? Please help me.