Java code example for SMTP

<dependency>
    <groupId>com.sun.mail</groupId>
    <artifactId>javax.mail</artifactId>
    <version>1.6.2</version>
</dependency>
<dependency>
    <groupId>javax.activation</groupId>
    <artifactId>activation</artifactId>
    <version>1.1.1</version>
</dependency>
<dependency>
    <groupId>com.google.code.gson</groupId>
    <artifactId>gson</artifactId>
    <version>2.8.6</version>
</dependency>

Sample code

package org.example;

import javax.mail.*;
import javax.mail.internet.*;
import java.io.UnsupportedEncodingException;
//import java.net.MalformedURLException;
import java.util.Date;
import java.util.Properties;
import java.util.UUID;
//import java.util.HashMap;
//import java.util.Base64;
//import java.net.URL;
//import java.io.IOException;
//import java.io.InputStream;
//import javax.mail.util.ByteArrayDataSource;
//import java.net.URLEncoder;
//import javax.activation.DataHandler;
//import javax.activation.FileDataSource;
//import javax.activation.URLDataSource;

//import com.google.gson.GsonBuilder;

public class SampleMail {
    // Configure constants.
    private static final String SMTP_HOST = "smtpdm.aliyun.com";
    private static final int SMTP_PORT = 80;
    private static final String USER_NAME = "your_sender_address";
    private static final String PASSWORD = "your_smtp_password";

    protected static String genMessageID(String mailFrom) {
        // Generate the Message-ID.
        if (!mailFrom.contains("@")) {
            throw new IllegalArgumentException("Invalid email format: " + mailFrom);
        }
        String domain = mailFrom.split("@")[1];
        UUID uuid = UUID.randomUUID();
        return "<" + uuid.toString() + "@" + domain + ">";
    }

    private static void setRecipients(MimeMessage message, Message.RecipientType type, String[] recipients)
            throws MessagingException {
        // Set recipient addresses.
        if (recipients == null || recipients.length == 0) {
            return; // Do not set if the list is empty.
        }
        InternetAddress[] addresses = new InternetAddress[recipients.length];
        for (int h = 0; h < recipients.length; h++) {
            addresses[h] = new InternetAddress(recipients[h]);
        }
        message.setRecipients(type, addresses);
    }

    public static void main(String[] args) throws MessagingException, UnsupportedEncodingException {
        // Configure email sending properties.
        final Properties props = new Properties();

        // Enable SMTP authentication.
        props.put("mail.smtp.auth", "true");
        props.put("mail.smtp.host", SMTP_HOST);
        // Set the port:
        props.put("mail.smtp.port", SMTP_PORT);// or "25". For SSL, remove the port 80/25 configuration and use the following settings instead:
        // Encryption method:
        //props.put("mail.smtp.socketFactory.class", "javax.net.ssl.SSLSocketFactory");
        //props.put("mail.smtp.socketFactory.fallback", "false");// Prevents fallback to non-encrypted connections.
        //props.put("mail.smtp.socketFactory.port", "465");
        //props.put("mail.smtp.port", "465");

        props.put("mail.smtp.from", USER_NAME);    // The mail.from parameter.
        props.put("mail.user", USER_NAME);// The sender account (the sender address created in the console).
        props.put("mail.password", PASSWORD);// The SMTP password for the sender address (set in the console).
        //props.put("mail.smtp.connectiontimeout", 1000);
        System.setProperty("mail.mime.splitlongparameters", "false");// Prevents display issues caused by excessively long attachment filenames.
        //props.put("mail.smtp.ssl.enable", "true");  // Use with port 465.
        //props.put("mail.smtp.ssl.protocols", "TLSv1.2");  // Specify the TLS version.

        // Create the authenticator for SMTP authentication.
        Authenticator authenticator = new Authenticator() {
            @Override
            protected PasswordAuthentication getPasswordAuthentication() {
                return new PasswordAuthentication(USER_NAME, PASSWORD);
            }
        };

        // Create a mail session using the properties and authenticator.
        Session mailSession = Session.getInstance(props, authenticator);

        String messageIDValue = genMessageID(USER_NAME);
        MimeMessage message = new MimeMessage(mailSession) {
            @Override
            protected void updateMessageID() throws MessagingException {
                setHeader("Message-ID", messageIDValue);
            }
        };

        try {
            // Set the sender's address and alias. The address must be configured in the console and match the 'mail.user' property. The alias is a custom display name.
            InternetAddress from = new InternetAddress(USER_NAME, "Your Sender Alias");
            message.setFrom(from);

            setRecipients(message, Message.RecipientType.TO, new String[]{"recipient_address_1", "recipient_address_2"});
            setRecipients(message, Message.RecipientType.CC, new String[]{"recipient_address_3", "recipient_address_4"});
            setRecipients(message, Message.RecipientType.BCC, new String[]{"recipient_address_5", "recipient_address_6"});

            InternetAddress replyToAddress = new InternetAddress("your_reply_to_address");
            message.setReplyTo(new Address[]{replyToAddress});// Optional. Set the reply-to address.
            message.setSentDate(new Date());
            message.setSubject("Test subject");
//            message.setContent("Test txt content 1", "text/plain;charset=UTF-8");// Plain text content. This is overwritten if you use MimeBodyPart.
//            or
//            message.setContent("Test<br> HTML content 2", "text/html;charset=UTF-8");// HTML content. This is overwritten if you use MimeBodyPart.

//            // To enable email tracking, set the X-AliDM-Trace header as shown below. For prerequisites and constraints, see the documentation on enabling data tracking.
//            String tagName = "your_tag_name";
//            HashMap<String, String> trace = new HashMap<>();
//            trace.put("OpenTrace", "1");      // Enable open tracking.
//            trace.put("LinkTrace", "1");     // Enable URL click tracking.
//            trace.put("TagName", tagName);   // The tag name created in the console.
//            String jsonTrace = new GsonBuilder().setPrettyPrinting().create().toJson(trace);
//            //System.out.println(jsonTrace);
//            String base64Trace = new String(Base64.getEncoder().encode(jsonTrace.getBytes()));
//            // Set the tracking header.
//            message.addHeader("X-AliDM-Trace", base64Trace);
            // Example value in the raw email (EML): X-AliDM-Trace: eyJUYWdOYW1lIjoiVGVzdCIsIk9wZW5UcmFjZSI6IjEiLCJMaW5rVHJhY2UiOiIxIn0=

            // Add content and attachments:
            // Create a multipart message.
            Multipart multipart = new MimeMultipart();

//            // Create a BodyPart for plain text content.
//            BodyPart textPart = new MimeBodyPart();
//            textPart.setText("Test txt content 3");
//            multipart.addBodyPart(textPart);

            // Create a BodyPart for HTML content.
            BodyPart htmlPart = new MimeBodyPart();
            htmlPart.setContent("Test<br> HTML content 4", "text/html;charset=UTF-8");// Set the email content. This overwrites the previous message.setContent call.
            multipart.addBodyPart(htmlPart);

//            // Add attachments.
//            // Create and add attachment parts. The total email size, including attachments, cannot exceed 15 MB.
//            // Send local attachments.
//            String[] fileList = {"C:\\Users\\Downloads\\test1.txt", "C:\\Users\\Downloads\\test2.txt"};
//            for (String filePath : fileList) {
//                MimeBodyPart mimeBodyPart = new MimeBodyPart();
//
//                FileDataSource fileDataSource = new FileDataSource(filePath);
//                mimeBodyPart.setDataHandler(new DataHandler(fileDataSource));
//                // Encode the attachment filename to prevent garbled characters.
//                mimeBodyPart.setFileName(MimeUtility.encodeWord(fileDataSource.getName()));
//                mimeBodyPart.addHeader("Content-Transfer-Encoding", "base64");
//                multipart.addBodyPart(mimeBodyPart);
//            }


//            // Send attachments from a URL.
//            String[] fileListUrl = {"https://example.oss-cn-shanghai.aliyuncs.com/xxxxxxxxxxx1.png", "https://example.oss-cn-shanghai.aliyuncs.com/xxxxxxxxxxx2.png"};
//            for (String fileUrl : fileListUrl) {
//                URL url = new URL(fileUrl);
//                String filename = url.getPath();
//                filename = filename.substring(filename.lastIndexOf('/') + 1);
//                try (InputStream in = url.openStream()) {
//                    // Create an attachment part.
//                    MimeBodyPart attachmentPart = new MimeBodyPart();
//                    // Use a byte array data source.
//                    ByteArrayDataSource ds = new ByteArrayDataSource(in, "application/octet-stream");
//                    attachmentPart.setDataHandler(new javax.activation.DataHandler(ds));
//                    attachmentPart.setFileName(filename);
//                    attachmentPart.setDisposition(MimeBodyPart.ATTACHMENT);
//                    multipart.addBodyPart(attachmentPart);
//                } catch (IOException e) {
//                    throw new RuntimeException(e);
//                }
//            }

            // Set the multipart content for the message.
            message.setContent(multipart);
            // End of the code for sending attachments.

            //mailSession.setDebug(true);// Enable debug mode.
            Transport.send(message);
            System.out.println("Email sent successfully!");
        } catch (MessagingException | UnsupportedEncodingException e) {
            System.err.println("Failed to send the email: " + e.getMessage());
            e.printStackTrace();
//        } catch (MalformedURLException e) {
//            throw new RuntimeException(e);
        }

    }

}

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