JavaMail 是 Java 平台發送郵件的標準 API。本文涵蓋 Maven 依賴、簡單文本郵件、HTML 富文本、多附件、內嵌圖片、SSL/TLS 加密連接、QQ/163/Gmail 郵箱授權碼配置、異步發送線程池封裝，助你快速接入郵件通知能力。

一、Maven 依賴 (Jakarta Mail 2.0+)

    com.sun.mail
    jakarta.mail
    2.0.1



    com.sun.mail
    javax.mail
    1.6.2

二、核心配置屬性

三、三大發送模式完整代碼

1. 簡單文本郵件

public void sendText(String to, String subject, String content) {
    Properties props = buildProps();
    Session session = Session.getInstance(props, new Authenticator() {
        protected PasswordAuthentication getPasswordAuthentication() {
            return new PasswordAuthentication(USERNAME, PASSWORD);
        }
    });
    try {
        MimeMessage msg = new MimeMessage(session);
        msg.setFrom(new InternetAddress(FROM));
        msg.setRecipient(Message.RecipientType.TO, new InternetAddress(to));
        msg.setSubject(subject, "UTF-8");
        msg.setText(content, "UTF-8");
        Transport.send(msg);
    } catch (MessagingException e) { throw new RuntimeException(e); }
}

2. HTML 富文本郵件

msg.setContent("
歡迎註冊
您的驗證碼: 123456
", "text/html;charset=UTF-8");

3. 多附件 + 內嵌圖片 (MimeMultipart)

public void sendWithAttachments(String to, String subject, String html, 
                                List attachments, Map inlineImages) {
    MimeMessage msg = new MimeMessage(session);
    msg.setFrom(new InternetAddress(FROM));
    msg.setRecipients(Message.RecipientType.TO, to);
    msg.setSubject(subject, "UTF-8");

    // 根容器: mixed (附件) -> related (內嵌圖片+HTML) -> alternative (文本/HTML)
    MimeMultipart mixed = new MimeMultipart("mixed");
    MimeMultipart related = new MimeMultipart("related");
    MimeMultipart alternative = new MimeMultipart("alternative");

    // 文本版本 (可選)
    MimeBodyPart textPart = new MimeBodyPart();
    textPart.setText("純文本備選內容", "UTF-8");
    alternative.addBodyPart(textPart);

    // HTML 版本
    MimeBodyPart htmlPart = new MimeBodyPart();
    htmlPart.setContent(html, "text/html;charset=UTF-8");
    alternative.addBodyPart(htmlPart);

    related.addBodyPart(alternative);

    // 內嵌圖片
    for (Map.Entry e : inlineImages.entrySet()) {
        MimeBodyPart imgPart = new MimeBodyPart();
        imgPart.attachFile(e.getValue());
        imgPart.setContentID("<" + e.getKey() + ">"); // HTML 中 
        imgPart.setDisposition(MimeBodyPart.INLINE);
        related.addBodyPart(imgPart);
    }

    MimeBodyPart relatedWrapper = new MimeBodyPart();
    relatedWrapper.setContent(related);
    mixed.addBodyPart(relatedWrapper);

    // 附件
    for (File file : attachments) {
        MimeBodyPart att = new MimeBodyPart();
        att.attachFile(file);
        att.setFileName(MimeUtility.encodeText(file.getName(), "UTF-8", "B")); // 編碼中文文件名
        mixed.addBodyPart(att);
    }

    msg.setContent(mixed);
    Transport.send(msg);
}

四、主流郵箱 SMTP 配置對照表

五、QQ 郵箱實戰完整類

public class QQMailSender {
    private static final String HOST = "smtp.qq.com";
    private static final String USER = "your_qq@qq.com";
    private static final String AUTH_CODE = "your_16_digit_auth_code"; // 授權碼，非登錄密碼
    private static final String FROM = "your_qq@qq.com";

    public static void main(String[] args) {
        Properties props = new Properties();
        props.put("mail.smtp.host", HOST);
        props.put("mail.smtp.port", "465");
        props.put("mail.smtp.auth", "true");
        props.put("mail.smtp.ssl.enable", "true");
        props.put("mail.debug", "true");

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

        try {
            MimeMessage msg = new MimeMessage(session);
            msg.setFrom(new InternetAddress(FROM));
            msg.addRecipient(Message.RecipientType.TO, new InternetAddress("target@example.com"));
            msg.setSubject("JavaMail 測試", "UTF-8");
            msg.setText("這是一封來自 Java 的測試郵件。", "UTF-8");
            Transport.send(msg);
            System.out.println("發送成功");
        } catch (MessagingException e) {
            e.printStackTrace();
        }
    }
}

六、生產級封裝建議

1. 連接池：使用 com.sun.mail.smtp.SMTPTransport 連接池或 Spring JavaMailSenderImpl + spring.mail 配置。
2. 異步發送：@Async + 線程池，避免阻塞業務線程；結合消息隊列實現重試、降級、幂等。
3. 模板引擎：Thymeleaf/FreeMarker 渲染 HTML 模板，分離代碼與內容。
4. 發送記錄表：持久化郵件主題、收件人、狀態、重試次數、錯誤信息，便於排查與補發。
5. 頻率限制：單 IP/賬號/域名頻率控制，防止被郵箱服務商封禁。