How to configure SMTP authentication

Hi all,  I am writting a program which will send emails with attachments to myself.
I am trying to configure the server to use basic windows authhentication but i can't. I get the 
Untitled PageSystem.Net.Mail.SmtpException: The SMTP server requires a secure connection or the client was not authenticated.
all the time.
When I use allow anonymous access everything works ok.
My code is this:
  MailAddress from = new MailAddress("from@address");
          MailAddress to = new MailAddress("to@address");
            MailMessage message = new MailMessage(from, to);
            message.Subject = "This is a test email.";
            message.Body = @"body of the email& ...