title: MailBox UnAvailable 5.7.1. The server response was: 5.7.1 Unable to relay
body: <p>Below code is working fine if I send mails which are in xyz.rw domain (like abcd@xyz.rw, test@xyz.rw). When I tried to send mail to my gmail account, below error occurred. Its not working for other domain mail ids</p>
  
  <blockquote>
    <p>MailBox Unavailable 5.7.1. The server response was: 5.7.1 Unable to
    relay</p>
  </blockquote>
  
  <p>Please let me know how to fix this.</p>
  
  <pre><code>SmtpClient smtp = new SmtpClient();
  smtp.Port = 25;
  smtp.Host = "10.8.12.242";
  smtp.UseDefaultCredentials = false;
  smtp.EnableSsl = false;
  smtp.DeliveryMethod = SmtpDeliveryMethod.Network;
  smtp.Credentials = new System.Net.NetworkCredential(senderID, senderPassword);
  smtp.Timeout = 30000;
  
  MailMessage message = new MailMessage(senderID, "abcd@xyz.rw", "Information Entreprise", "Hello, that message has been sent as consiquence of mail sending test.");
  try
  {
      smtp.Send(message);
  }
  catch (Exception ex)
  {
      MessageBox.Show(ex.Message);
  }
  </code></pre>