Using JavaMail with TLS

We actually have some notification code in our product that uses TLS to send mail if it is available.

You will need to set the Java Mail properties. You only need the TLS one but you might need SSL if your SMTP server uses SSL.

Properties props = new Properties();
props.put("mail.smtp.starttls.enable","true");
props.put("mail.smtp.auth", "true");  // If you need to authenticate
// Use the following if you need SSL
props.put("mail.smtp.socketFactory.port", d_port);
props.put("mail.smtp.socketFactory.class", "javax.net.ssl.SSLSocketFactory");
props.put("mail.smtp.socketFactory.fallback", "false");

You can then either pass this to a JavaMail Session or any other session instantiator like Session.getDefaultInstance(props).

Good post, the line

props.put("mail.smtp.socketFactory.class", "javax.net.ssl.SSLSocketFactory");

is mandatory if the SMTP server uses SSL Authentication, like the GMail SMTP server does. However if the server uses Plaintext Authentication over TLS, it should not be present, because Java Mail will complain about the initial connection being plaintext.

Also make sure you are using the latest version of Java Mail. Recently I used some old Java Mail jars from a previous project and could not make the code work, because the login process was failing. After I have upgraded to the latest version of Java Mail, the reason of the error became clear: it was a javax.net.ssl.SSLHandshakeException, which was not thrown up in the old version of the lib.

I just spent quite a bit of time figuring out how to use JavaMail to send emails with gmail or office365. I couldn't find the answer in the faq, but was helped a bit by the javadoc.

If you forget props.put("mail.smtp.starttls.enable","true") you get com.sun.mail.smtp.SMTPSendFailedException: 451 5.7.3 STARTTLS is required to send mail.

If you forget props.put("mail.smtp.ssl.protocols", "TLSv1.2"); you get javax.mail.MessagingException: Could not convert socket to TLS; and No appropriate protocol (protocol is disabled or cipher suites are inappropriate). Apparently this is only necessary for JavaMail versions 1.5.2 and older.

Here is the minimal code I required to get it to work:

import java.util.Properties;
import javax.mail.Authenticator;
import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.PasswordAuthentication;
import javax.mail.Session;
import javax.mail.Transport;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;

public class SendEmail {
    public static void main(String[] args) {
        Properties props = new Properties();
        props.put("mail.smtp.auth", "true");
        props.put("mail.smtp.starttls.enable","true");
        // smtp.gmail.com supports TLSv1.2 and TLSv1.3
        // smtp.office365.com supports only TLSv1.2
        props.put("mail.smtp.ssl.protocols", "TLSv1.2");
        props.put("mail.smtp.host", "smtp.office365.com");
        props.put("mail.smtp.port", "587");
        
        Session session = Session.getInstance(props, new Authenticator() {
            @Override
            protected PasswordAuthentication getPasswordAuthentication() {
                return new PasswordAuthentication("test@example.com", "******");
            }
        });
        
        try {
            Message message = new MimeMessage(session);
            message.setFrom(new InternetAddress("sender@example.com"));
            message.setRecipients(Message.RecipientType.TO, InternetAddress.parse("recipient@example.com"));
            message.setSubject("You got mail");
            message.setText("This email was sent with JavaMail.");
            Transport.send(message);
            System.out.println("Email sent.");
        } catch (MessagingException e) {
            throw new RuntimeException(e);
        }
    }
}

As a small note, it only started to work for me when I changed smtp to smtps in the examples above per samples from javamail (see smtpsend.java, https://github.com/javaee/javamail/releases/download/JAVAMAIL-1_6_2/javamail-samples.zip, option -S).

My resulting code is as follow:

Properties props=new Properties();
props.put("mail.smtps.starttls.enable","true");
// Use the following if you need SSL
props.put("mail.smtps.socketFactory.port", port);
props.put("mail.smtps.socketFactory.class", "javax.net.ssl.SSLSocketFactory");
props.put("mail.smtps.socketFactory.fallback", "false");
props.put("mail.smtps.host", serverList.get(randNum));
Session session = Session.getDefaultInstance(props);

smtpConnectionPool = new SmtpConnectionPool(
    SmtpConnectionFactories.newSmtpFactory(session));
    
final ClosableSmtpConnection transport = smtpConnectionPool.borrowObject();
...
transport.sendMessage(message, message.getAllRecipients());