public class ReadEmailStep {

    public static void main(String[] args) {

        // for smtp
        // String host = "smtp.gmail.com";// change accordingly
        // String mailStoreType = "imaps";

        // for pop3
        String host = "pop.gmail.com";
        String mailStoreType = "pop3s";

        String username = "<email_address>";// change accordingly
        String password = "<password>";// change accordingly
        String folder = "INBOX";
        readMessages(host, mailStoreType, username, password, folder);

    }

    private static void addPop3Props(Properties properties, String host, String port) {
        properties.setProperty("mail.pop3.host", host);
        properties.setProperty("mail.pop3.port", port);
        properties.setProperty("mail.pop3.socketFactory.class", "javax.net.ssl.SSLSocketFactory");
        properties.setProperty("mail.pop3.socketFactory.port", port);
        properties.setProperty("mail.pop3.starttls.enable", "true");
        properties.setProperty("mail.pop3.socketFactory.fallback", "false");
        properties.setProperty("mail.pop3.rsetbeforequit", "true");
    }

    private static void addSmtpProps(Properties properties, String host, String port) {
        properties.setProperty("mail.smtp.host", host);
        properties.setProperty("mail.smtp.socketFactory.port", port);
        properties.setProperty("mail.smtp.port", port);
        properties.setProperty("mail.smtp.socketFactory.class", "javax.net.ssl.SSLSocketFactory");
        properties.setProperty("mail.smtp.auth", "true");
    }

    public static void readMessages(String host, String storeType, String user, String password, String folder) {
        try {

            // create properties field
            Properties properties = new Properties();

            if (storeType.equals("pop3s")) {
                addPop3Props(properties, host, "995");
            } else if (storeType.equals("imaps")){
                addSmtpProps(properties, host, "465");
            } else {
                throw new Exception("unknown storeType: " + storeType);
            }

            URLName url = new URLName(storeType, host, 995, "",  user, password);
            Session session = Session.getInstance(properties, null);
            Store store = new POP3SSLStore(session, url);
            store.connect();

           //Session emailSession = Session.getDefaultInstance(properties, null);
           //Store store = emailSession.getStore(storeType);

            store.connect(host, user, password);

            // create the folder object and open it
            Folder emailFolder = store.getFolder(folder);
            emailFolder.open(Folder.READ_ONLY);

            // retrieve the messages from the folder in an array and print it
            Message[] messages = emailFolder.getMessages();
            System.out.println("messages.length---" + messages.length);

            //  do something with messages

            // close the store and folder objects
            emailFolder.close(false);
            store.close();

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

javax.mail.MessagingException: Connect failed;
  nested exception is:
    java.net.ConnectException: Connection refused: connect
    at com.sun.mail.pop3.POP3Store.protocolConnect(POP3Store.java:120)
    at javax.mail.Service.connect(Service.java:233)
    at javax.mail.Service.connect(Service.java:134)
    at javax.mail.Service.connect(Service.java:86)
    at com.smartstream.control.engine.custom.ReadEmailStep.readMessages(ReadEmailStep.java:71)
    at com.smartstream.control.engine.custom.ReadEmailStep.main(ReadEmailStep.java:32)