title: Mail sending Error c#
body: <p>How to solve this SMTP Error problem? When I'm sending mail I'm facing this error message. Sending mail using local system is not a problem. Does anyone know the solution to this problem?</p>
  
  <blockquote>
    <p>System.Net.Mail.SmtpException: The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.1 Authentication Required.<br>
    at System.Net.Mail.MailCommand.CheckResponse(SmtpStatusCode statusCode, String response)<br>
    at System.Net.Mail.MailCommand.Send(SmtpConnection conn, Byte[] command, MailAddress from, Boolean allowUnicode)<br>
    at System.Net.Mail.SmtpTransport.SendMail(MailAddress sender, MailAddressCollection recipients, String deliveryNotify, Boolean allowUnicode, SmtpFailedRecipientException&amp; exception)<br>
    at System.Net.Mail.SmtpClient.Send(MailMessage message)<br>
    at admin_booking.btninvoicemail_Click(Object sender, EventArgs e) in c:\inetpub\vhosts\starlineroadways.com\httpdocs\admin_booking.aspx.cs:line 596
    code:</p>
  </blockquote>
  
  <pre><code>System.Net.Mail.SmtpClient smtp = new System.Net.Mail.SmtpClient();
  smtp.Host = "smtp.gmail.com";
  smtp.EnableSsl = true;
  smtp.DeliveryMethod = SmtpDeliveryMethod.Network;
  smtp.Credentials = new System.Net.NetworkCredential("xx@gmail.com", "xx");  
  System.Net.Mail.MailMessage oMsg = new System.Net.Mail.MailMessage();
  MailAddress @add = new MailAddress(txtsendemail.Text);  
  oMsg.From = new MailAddress("xx");
  oMsg.To.Add(@add);
  oMsg.Subject = "xxx";
  oMsg.Body = msgbody2;
  oMsg.IsBodyHtml = true;
  smtp.Send(oMsg);
  </code></pre>