How do I debug application that uses JavaMail APIs?

To ask Java mail to print out a debug message when you run a Java mail program you can add the mail.debug and set the value to true into the properties used to create the session object.

The other way is to set the debug setting of the session using the session.setDebug() method and pass true as the parameter. This will also turn on the debug message in your Java mail program.

package org.kodejava.mail;

import javax.mail.*;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;
import java.util.Date;
import java.util.Properties;

public class MailDebugDemo {
    public static void main(String[] args) {
        MailDebugDemo.sendMail("kodejava@gmail.com", "kodejava@gmail.com",
                "Debug Demo", "Mail Debug Demo");
    }

    private static void sendMail(String mailFrom, String mailTo, String mailSubject,
                                 String mailText) {
        Properties props = new Properties() {{
            put("mail.smtp.auth", "true");
            put("mail.smtp.host", "smtp.gmail.com");
            put("mail.transport.protocol", "smtp");
            put("mail.smtp.port", "587");
            put("mail.smtp.starttls.enable", "true");
            put("mail.smtp.ssl.protocols", "TLSv1.2");
            put("mail.debug", "true");
        }};

        // Creates a mail session. We need to supply username and
        // password for GMail authentication.
        Session session = Session.getInstance(props, new Authenticator() {
            @Override
            protected PasswordAuthentication getPasswordAuthentication() {
                return new PasswordAuthentication("kodejava@gmail.com", "password");
            }
        });

        try {
            // Creates email message
            Message message = new MimeMessage(session);
            message.setSentDate(new Date());
            message.setFrom(new InternetAddress(mailFrom));
            message.setRecipient(Message.RecipientType.TO,
                    new InternetAddress(mailTo));
            message.setSubject(mailSubject);
            message.setText(mailText);

            // Send a message
            Transport.send(message);
        } catch (MessagingException e) {
            e.printStackTrace();
        }
    }
}

Here is an example of debug information produce by the JavaMail API when sending an email using Gmail SMTP server.

DEBUG: JavaMail version 1.5.6
DEBUG: successfully loaded resource: /META-INF/javamail.default.providers
DEBUG: Tables of loaded providers
DEBUG: Providers Listed By Class Name: {com.sun.mail.smtp.SMTPSSLTransport=javax.mail.Provider[TRANSPORT,smtps,com.sun.mail.smtp.SMTPSSLTransport,Oracle], com.sun.mail.smtp.SMTPTransport=javax.mail.Provider[TRANSPORT,smtp,com.sun.mail.smtp.SMTPTransport,Oracle], com.sun.mail.imap.IMAPSSLStore=javax.mail.Provider[STORE,imaps,com.sun.mail.imap.IMAPSSLStore,Oracle], com.sun.mail.pop3.POP3SSLStore=javax.mail.Provider[STORE,pop3s,com.sun.mail.pop3.POP3SSLStore,Oracle], com.sun.mail.imap.IMAPStore=javax.mail.Provider[STORE,imap,com.sun.mail.imap.IMAPStore,Oracle], com.sun.mail.pop3.POP3Store=javax.mail.Provider[STORE,pop3,com.sun.mail.pop3.POP3Store,Oracle]}
DEBUG: Providers Listed By Protocol: {imaps=javax.mail.Provider[STORE,imaps,com.sun.mail.imap.IMAPSSLStore,Oracle], imap=javax.mail.Provider[STORE,imap,com.sun.mail.imap.IMAPStore,Oracle], smtps=javax.mail.Provider[TRANSPORT,smtps,com.sun.mail.smtp.SMTPSSLTransport,Oracle], pop3=javax.mail.Provider[STORE,pop3,com.sun.mail.pop3.POP3Store,Oracle], pop3s=javax.mail.Provider[STORE,pop3s,com.sun.mail.pop3.POP3SSLStore,Oracle], smtp=javax.mail.Provider[TRANSPORT,smtp,com.sun.mail.smtp.SMTPTransport,Oracle]}
DEBUG: successfully loaded resource: /META-INF/javamail.default.address.map
DEBUG: getProvider() returning javax.mail.Provider[TRANSPORT,smtp,com.sun.mail.smtp.SMTPTransport,Oracle]
DEBUG SMTP: useEhlo true, useAuth true
DEBUG SMTP: useEhlo true, useAuth true
DEBUG SMTP: trying to connect to host "smtp.gmail.com", port 587, isSSL false
220 smtp.gmail.com ESMTP b2sm4488826pgh.33 - gsmtp
DEBUG SMTP: connected to host "smtp.gmail.com", port: 587
...
...

Maven Dependencies

<dependencies>
    <!-- https://search.maven.org/remotecontent?filepath=javax/mail/javax.mail-api/1.5.6/javax.mail-api-1.5.6.jar -->
    <dependency>
        <groupId>javax.mail</groupId>
        <artifactId>javax.mail-api</artifactId>
        <version>1.5.6</version>
    </dependency>
    <!-- https://search.maven.org/remotecontent?filepath=javax/mail/mail/1.4.7/mail-1.4.7.jar -->
    <dependency>
        <groupId>javax.mail</groupId>
        <artifactId>mail</artifactId>
        <version>1.4.7</version>
    </dependency>
</dependencies>

Author
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Wayan

Founder at Kode Java Org

A programmer, runner, recreational diver, live in the island of Bali, Indonesia. Programming in Java, Spring, Hibernate / JPA. You can support me working on this project, buy me a cup of coffee ☕, every little bit helps, thank you 🙏

How do I debug application that uses JavaMail APIs?

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