JavaMail SMTPSendFailedException

I am writing a bulk email program using the JavaMail api. I have a Microsoft Exhange server which I am trying to send the emails in to. When I run my program I get the following error:

**com.sun.mail.smtp.SMTPTransport.issueSendCommand(SMTPTransport.java:2057)
at com.sun.mail.smtp.SMTPTransport.finishData(SMTPTransport.java:1862)
at com.sun.mail.smtp.SMTPTransport.sendMessage(SMTPTransport.java:1100)
at javax.mail.Transport.send0(Transport.java:195)
at javax.mail.Transport.send(Transport.java:124)
at SendEmail.postMail(SendEmail.java:100)
at EmailGenerator.main(EmailGenerator.java:52)**

The part of my code trying to send the message is as follows:

Properties props = new Properties();
props.put("mail.smtp.host", email_server);
props.put("mail.transport.protocol", "smtp");
props.put("mail.smtp.auth", true);

class EmailAuthenticator extends Authenticator {
String user;
String pw;
EmailAuthenticator (String FROM, String PASSWORD)
{
    super();
    this.user = FROM;
    this.pw = PASSWORD;
}
public PasswordAuthentication getPasswordAuthentication()
{
    return new PasswordAuthentication(user, pw);
}
}

Session session = Session.getInstance(props, new EmailAuthenticator(USER, PASSWORD));
session.setDebug(debug);
System.out.println("Session created");

.. CREATED MESSAGE HERE...

Transport transport = session.getTransport("smtp");
transport.connect(exchange_server,user,password);
transport.send(msg);
transport.close();

I wonder am I missing some configuration on the Exchange server side, or is an issue with my code?

OK I figured out where I was going wrong here and am posting up the answer incase anybody else can get some value out of it. I had the following line of code:

props.put("mail.smtp.auth", true);

This was telling my application that it needed to authenticate to the SMTP server, when in fact it didnt. This was causing my application from logging into the SMTP server and sending the email and thus producing the error message. Setting this property to false or not having this line of code fixed the issue for me. This line of code is only necessary for SMTP servers that require you to login, which my Exchange server didnt.