JavaMail: How to tell if SMTP server requires authentication

Question

I am writing an application that sends notification emails. I have a configuration screen for the user to specify the SMTP hostname and optionally a username and password, and I want to validate the settings. Here is the code I am using to do this:
Properties props = new Properties();
props.put("mail.transport.protocol", "smtp");
if (mailUsername != null || mailPassword != null)
    props.put("mail.smtp.auth", "true");
Session session = Session.getInstance(props, null);
transport = session.getTransport();
transport.connect(mailHostname, mailUsername, mailPassword);
transport.close();This works if the user enters a username and password (whether they are valid or not), or if the username and password are empty but the SMTP server does not require authentication. However, if the server requires authentication and the username and password are empty, the call to transport.connect() succeeds, but the user will get an error later on when the app tries to actually send an email. I want to query the SMTP server to find out if authentication is required (not just supported), and inform the user when they are configuring the email settings. Is there any way to do this? I suppose I could try sending a test email to a dummy address, but I was hoping there would be a cleaner way.

Answer 1

Thanks for your help. This is what I ended up doing, and it seems to work. For anyone else interested, after the code above (before transport.close(), I try to send an empty email, which causes JavaMail to throw an IOException, which I ignore. If some other MessagingException occurs, then there is some other problem (authentication required, invalid from address, etc).
try
   // ...code from above...
   // Try sending an empty  message, which should fail with an
   // IOException if all other settings are correct.
   MimeMessage msg = new MimeMessage(session);
   if (mailFromAddress != null)
       msg.setFrom(new InternetAddress(mailFromAddress));
   msg.saveChanges();
   transport.sendMessage(msg,
       new InternetAddress[] {new InternetAddress("[email protected]")});
catch (MessagingException e)
    // IOException is expected, anything else (including subclasses
    // of IOException like UnknownHostException) is an error.
    if (!e.getNextException().getClass().equals(IOException.class))
        // Handle other exceptions
}Edited by: svattom on Jan 7, 2009 7:37 PM
Edited by: svattom on Jan 7, 2009 10:01 PM
Changed handling of subclasses of IOException like UnknownHostException