Java Code Example for mySMTP with Jakarta Mail

Use Jakarta Mail, the official Java mail API, to send email through mySMTP with STARTTLS on port 587. The reference implementation is Angus Mail.

Prerequisites

Java 11 or later
Maven or Gradle
Your mySMTP username and password from the setup email
Your mySMTP hostname from the setup email (shown as relayxx.mysmtp.com in these examples)

Install Angus Mail

<dependency>
    <groupId>org.eclipse.angus</groupId>
    <artifactId>angus-mail</artifactId>
    <version>2.0.3</version>
</dependency>

dependencies {
    implementation 'org.eclipse.angus:angus-mail:2.0.3'
}

Basic send example

import jakarta.mail.*;
import jakarta.mail.internet.*;
import java.util.Properties;

public class MySmtpExample {
    public static void main(String[] args) throws Exception {
        String host = System.getenv().getOrDefault("MYSMTP_HOST", "relayxx.mysmtp.com");
        String user = System.getenv("MYSMTP_USER");
        String pass = System.getenv("MYSMTP_PASS");

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

        Session session = Session.getInstance(props, new Authenticator() {
            @Override
            protected PasswordAuthentication getPasswordAuthentication() {
                return new PasswordAuthentication(user, pass);
            }
        });

        Message message = new MimeMessage(session);
        message.setFrom(new InternetAddress("you@yourdomain.com", "Your Name"));
        message.setRecipients(Message.RecipientType.TO,
            InternetAddress.parse("recipient@example.com"));
        message.setSubject("Test email from Java");
        message.setText("This is a plain text test message sent through mySMTP.");

        Transport.send(message);
        System.out.println("Message sent successfully");
    }
}

Replace relayxx.mysmtp.com with your real hostname from the mySMTP setup email. Load credentials from environment variables, never hardcode them in source files.

HTML email with attachment

import jakarta.mail.*;
import jakarta.mail.internet.*;
import java.util.Properties;

public class MySmtpHtmlExample {
    public static void main(String[] args) throws Exception {
        String host = System.getenv().getOrDefault("MYSMTP_HOST", "relayxx.mysmtp.com");
        String user = System.getenv("MYSMTP_USER");
        String pass = System.getenv("MYSMTP_PASS");

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

        Session session = Session.getInstance(props, new Authenticator() {
            @Override
            protected PasswordAuthentication getPasswordAuthentication() {
                return new PasswordAuthentication(user, pass);
            }
        });

        Message message = new MimeMessage(session);
        message.setFrom(new InternetAddress("you@yourdomain.com", "Your Name"));
        message.setRecipients(Message.RecipientType.TO,
            InternetAddress.parse("recipient@example.com"));
        message.setSubject("HTML email with attachment");

        MimeBodyPart textPart = new MimeBodyPart();
        textPart.setText("This is the plain text fallback.", "utf-8");

        MimeBodyPart htmlPart = new MimeBodyPart();
        htmlPart.setContent(
            "<h1>Hello</h1><p>This is an HTML message.</p>",
            "text/html; charset=utf-8"
        );

        MimeMultipart alternative = new MimeMultipart("alternative");
        alternative.addBodyPart(textPart);
        alternative.addBodyPart(htmlPart);

        MimeBodyPart attachmentPart = new MimeBodyPart();
        attachmentPart.attachFile("/path/to/invoice.pdf");

        MimeMultipart mixed = new MimeMultipart("mixed");
        mixed.addBodyPart(new MimeBodyPart() {{ setContent(alternative); }});
        mixed.addBodyPart(attachmentPart);

        message.setContent(mixed);
        Transport.send(message);
        System.out.println("Message sent successfully");
    }
}

Spring Boot application.properties

If you use Spring Boot, add these settings to application.properties:

spring.mail.host=${MYSMTP_HOST:relayxx.mysmtp.com}
spring.mail.port=587
spring.mail.username=${MYSMTP_USER}
spring.mail.password=${MYSMTP_PASS}
spring.mail.properties.mail.smtp.auth=true
spring.mail.properties.mail.smtp.starttls.enable=true

Inject JavaMailSender and call send(SimpleMailMessage) or send(MimeMessage).

Common errors

535 Authentication failed

Your username or password is incorrect, or your account is not yet activated. Re-enter credentials exactly as shown in the setup email. See Setting up SMTP credentials.

Connection timeout or refused

Your network or host may block port 587. Try port 2525 with the same properties, or port 465 with mail.smtp.ssl.enable=true. See Supported SMTP ports and encryption.

TLS handshake failure

The encryption properties do not match the port. Use mail.smtp.starttls.enable=true for ports 587 and 2525. Use mail.smtp.ssl.enable=true for port 465.

Test your SPF, DKIM, and DMARC setup with the mySMTP Deliverability Toolbox before sending large volumes.

Home

API & Webhooks

Java Code Example for mySMTP with Jakarta Mail

Prerequisites

Install Angus Mail

Basic send example

HTML email with attachment

Common errors

​Prerequisites

​Install Angus Mail

​Basic send example

​HTML email with attachment

​Common errors

​Related articles

Prerequisites

Install Angus Mail

Basic send example

HTML email with attachment

Common errors

Related articles