title: mail sending with network credential as true in windows form not working
body: <p>I want to do an application for sending emails in C# windows application.I used smtp server,but I don't want to set the network credentials. So I set it as true.but am getting error.</p>
  
  <blockquote>
    <p>The SMTP server requires a secure connection or the client was not
    authenticated. The server response was: 5.5.1 Authentication Required.
    Learn more at</p>
  </blockquote>
  
  <p>Here is the code:</p>
  
  <pre><code>SmtpClient oClient = new SmtpClient();
  oClient.Host = "smtp.gmail.com";
  oClient.Port = 25;
  oClient.UseDefaultCredentials = true;
  oClient.Credentials = new System.Net.NetworkCredential();
  oClient.EnableSsl = true;
  MailMessage oMail = new MailMessage();
  oMail.To.Add(txtTo.Text.Trim());
  oMail.From = new MailAddress("testmail@gmail.com");
  oMail.Subject = txtSubject.Text;
  oMail.Body = txtBody.Text;
  oMail.IsBodyHtml = true;
  oClient.Send(oMail);
  MessageBox.Show("Mail Send");
  </code></pre>
  
  <p>here I set the host as gmail.com,I need to send and receive mails using all email service providers.So how can I set the host and port?</p>