mail.java

final String username = "username@gmail.com";
final String password = "password";

Properties props = new Properties();
props.put("mail.smtp.auth", "true");
props.put("mail.smtp.starttls.enable", "true");
props.put("mail.smtp.host", "smtp.gmail.com");
props.put("mail.smtp.port", "587");

Session session = Session.getInstance(props,
  new javax.mail.Authenticator() {
    protected PasswordAuthentication getPasswordAuthentication() {
        return new PasswordAuthentication(username, password);
    }
  });

try {

    Message message = new MimeMessage(session);
    message.setFrom(new InternetAddress("from-email@gmail.com"));
    message.setRecipients(Message.RecipientType.TO,
        InternetAddress.parse("to-email@gmail.com"));
    message.setSubject("Testing Subject");
    message.setText("Dear Mail Crawler,"
        + "\n\n No spam to my email, please!");

    Transport.send(message);

    System.out.println("Done");

} catch (MessagingException e) {
    throw new RuntimeException(e);
}