TLS issue when sending to gmail through JavaMail
Exception in thread "main" com.sun.mail.smtp.SMTPSendFailedException: 530 5.7.0 Must issue a STARTTLS command first. l10sm302158wfk.21
     at com.sun.mail.smtp.SMTPTransport.issueSendCommand(SMTPTransport.java:2057)
     at com.sun.mail.smtp.SMTPTransport.mailFrom(SMTPTransport.java:1580)
     at com.sun.mail.smtp.SMTPTransport.sendMessage(SMTPTransport.java:1097)
     at SendEmail.main(SendEmail.java:47)

Properties props = new Properties();
    props.put("mail.transport.protocol", "smtp");
    props.put("mail.host", "smtp.gmail.com");
    props.put("mail.user", "blahblah@gmail.com");
    props.put("mail.password", "blah");
    props.put("mail.port", "587");

    Session mailSession = Session.getDefaultInstance(props, null);
    Transport transport = mailSession.getTransport();

    MimeMessage message = new MimeMessage(mailSession);
    message.setSubject("This is a test");
    message.setContent("This is a test", "text/plain");
    message.addRecipient(Message.RecipientType.TO, new InternetAddress("blahblah2@gmail.com"));

    transport.connect();
    transport.sendMessage(message, message.getRecipients(Message.RecipientType.TO));
    transport.close();

props.put("mail.smtp.starttls.enable", "true");

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

public class CopyOfSendMail {

private static String SMPT_HOSTNAME = "my smtp port no";
private static String USERNAME = "root";
private static String PASSWORD = "root";

public static void main(String[] args) {
    Properties props = new Properties();
    props.put("mail.smtp.host", SMPT_HOSTNAME);
    props.put("mail.from","aaa@gmail.com");
    props.put("mail.smtp.starttls.enable", "true");
    props.put("mail.smtp.auth", "true");
    props.put("mail.debug", "true");

    Session session = Session.getInstance(props, new Authenticator() {
        @Override
        protected PasswordAuthentication getPasswordAuthentication() {
            return new PasswordAuthentication(USERNAME, PASSWORD);
        }
    });
    try {
        MimeMessage msg = new MimeMessage(session);
        msg.setFrom();
        msg.setRecipients(Message.RecipientType.TO,
                          "bbb@gmail.com");
        msg.setSubject("JavaMail hello world example");
        msg.setSentDate(new Date());
        msg.setText("Hello, world!n");
        Transport.send(msg);
     } catch (MessagingException mex) {
        System.out.println("send failed, exception: " + mex);
     }
    }
}