title: The server response was: 4.3.2 Service not available, closing transmission channel
body: <p>I am getting this error while sending email from my application. Can anyone suggest any solution.</p>
  
  <blockquote>
    <p>Service not available, closing transmission channel. The server
    response was: 4.3.2 Service not available, closing transmission
    channel</p>
  </blockquote>
  
  <p>Below is code.</p>
  
  <pre><code>string adminID = "AAA@tu.edu";
  MailMessage msg = new MailMessage();
  msg.From = new MailAddress(adminID);
  msg.To.Add("BBB@ttu.edu");
  msg.Subject = "Sample Email";
  msg.Body = "Hello ";
  SmtpClient SmtpMail = new SmtpClient();
  SmtpMail.Host = "basic.smtp.ttu.edu";
  SmtpMail.Port = 25;
  SmtpMail.Send(msg);
  </code></pre>