Java EE (Java Enterprise Edition) General Discussion

I have the following sample program that sends email. But how do I make sure the email is delivered successfully to the recipient. I want to make sure assuming all the email addresses are valid want to check if email is delivered successfully. As currently it delivers email sometimes and sometimes I don't get email. Using MS Exchange.

package email;

import java.util.*;
import javax.mail.*;
import javax.mail.internet.*;
import javax.activation.*;
import javax.mail.event.*;

// Send a simple, single part, text/plain e-mail
public class TestEmail implements ConnectionListener, TransportListener{
    private static final String SMTP_HOST_NAME = "mail.somedomain.com";
    private static final String SMTP_AUTH_USER = "user@somedomain.com";
    private static final String SMTP_AUTH_PWD  = "password";
    
    public static void main(String[] args) {
        TestEmail te = new TestEmail();
        
        // SUBSTITUTE YOUR EMAIL ADDRESSES HERE!!!
        String to = "user12@yahoo.com";
        String from = "user@somedomain.com";
        // SUBSTITUTE YOUR ISP'S MAIL SERVER HERE!!!
        String host = "mail.somedomain.com";

        // Create properties, get Session
        Properties props = new Properties();

        // If using static Transport.send(),
        // need to specify which host to send it to
        props.put("mail.smtp.host", host);
        //props.put("mail.smtp.port", "25");
        props.put("mail.smtp.auth", "true");
        // To see what is going on behind the scene
        //props.put("mail.debug", "true");
        te.go(props, from, to);
    }
    
    public TestEmail() {}
    
    public void go(Properties props, String from, String to) {
        Authenticator auth = new SMTPAuthenticator();
        Session session = Session.getDefaultInstance(props, auth);
        //Session session = Session.getInstance(props);
        try {
            Transport trans = null;
            // Instantiatee a message
            Message msg = new MimeMessage(session);

            //Set message attributes
            msg.setFrom(new InternetAddress(from));
            InternetAddress[] address = {new InternetAddress(to)};
            msg.setRecipients(Message.RecipientType.TO, address);
            msg.setSubject("Test E-Mail through Java");
            msg.setSentDate(new Date());

            // Set message content
            msg.setText("This is a test of sending a " +
                        "plain text e-mail through Java.\n" +
                        "Here is line 2.");
            // get the smtp transport for the address
            trans = session.getTransport(address[0]);

            // register ourselves as listener for ConnectionEvents 
            // and TransportEvents
            trans.addConnectionListener(this);
            trans.addTransportListener(this);
            
            // connect the transport
            trans.connect();

            // send the message
            trans.sendMessage(msg, address);
            //Send the message
            //trans.send(msg);
        }
        catch (MessagingException mex) 
        {
            // Prints all nested (chained) exceptions as well
            mex.printStackTrace();
        }
    }
    public void messageDelivered(TransportEvent e) 
    {
        System.out.println("****** DEBUG messageDelivered");
    }
    
    public void messageNotDelivered(TransportEvent e) 
    {
        System.out.println("****** DEBUG messageNotDelivered");   
    }
    
    public void messagePartiallyDelivered(TransportEvent e) 
    {
        System.out.println("****** DEBUG messagePartiallyDelivered");    
    }
    
    public void closed(ConnectionEvent e) 
    {
        System.out.println("****** DEBUG closed");    
    }
    
    public void disconnected(ConnectionEvent e) 
    {
        System.out.println("****** DEBUG disconnect");    
    }
    
    public void opened(ConnectionEvent e) 
    {
        System.out.println("****** DEBUG opened");    
    }
    
    /**
    * SimpleAuthenticator is used to do simple authentication
    * when the SMTP server requires it.
    */
    private class SMTPAuthenticator extends javax.mail.Authenticator
    {

        public PasswordAuthentication getPasswordAuthentication()
        {
            String username = SMTP_AUTH_USER;
            String password = SMTP_AUTH_PWD;
            return new PasswordAuthentication(username, password);
        }
    }
}//End of class

Thanks