5.7.3 Requested action aborted; user not authenticated

Hi all,

I am trying to send to write a code to send email, but I'am getting this error :

5.7.3 Requested action aborted; user not authenticated

Here is my code, and I need your help

        MailMessage email = new MailMessage(strFrom,strTo);
        email.Subject = strObj;
        email.Body = strBody;
        email.Priority = MailPriority.High;
        SmtpClient client = new SmtpClient();
        client.EnableSsl = true;
  
        try
        {
    &nb ...