code for sending online email

MailMessage MailMesaji = new MailMessage();
 MailMesaji.Subject = "Hello";
 MailMesaji.Body = " How are u";
 MailMesaji.BodyEncoding = Encoding.GetEncoding("Windows-1254");
 MailMesaji.From = new MailAddress("Email Sender @ Domain");
 MailMesaji.To.Add(new MailAddress("Email Reciever @ Domain"));
 SmtpClient Smtp = new SmtpClient("smtp.mail.yahoo.com");
 OpenFileDialog Ofd = new OpenFileDialog();
 if (Ofd.ShowDialog() == DialogResult.OK)
 {
 string Att = Ofd.FileName;
 Attachment ATTa = new Attachment(Att);
 MailMesaji.Attachments.Add(ATTa);
  
 }
  
 Smtp.Credentials = new System.Net.NetworkCredential("Email Sender @ Domain", "PWD");
 Smtp.Send(MailMesaji);
 MessageBox.Show("mail Send");