解决发送批量邮件中包含无效邮件地址时而导致全部失败

问题

发送邮件时，地址中如果包含一个无效的邮件地址（地址是合法的，但该邮件地址不存在，比如说人员离职导致的邮件地址不存在），就会得到如下错误，从而导致整个发送失败。

org.springframework.mail.MailSendException: Failed messages: javax.mail.SendFailedException: Invalid Addresses; 
  nested exception is: 
    com.sun.mail.smtp.SMTPAddressFailedException: 550 Mailbox not found or access denied at 
    org.springframework.mail.javamail.JavaMailSenderImpl.doSend(JavaMailSenderImpl.java:490) at 
    org.springframework.mail.javamail.JavaMailSenderImpl.send(JavaMailSenderImpl.java:360) at 
    org.springframework.mail.javamail.JavaMailSenderImpl.send(JavaMailSenderImpl.java:355) at 

问题解决

很多时候我们希望发送邮件时即使发送列表中存在无效的邮件地址，但其他的有效邮件地址能够被正常投递出去。

public class MailSendHelper {
    /**
     * 邮件发送
     * @param mailTos     接收人
     * @param mailCcs     抄送人
     * @param subject     主题
     * @param content     内容
     * @param personal    显示名称
     * @param attachments 附件
     * @param user        发件人
     * @param pwd         密码
     * @return
     */
    public static MailSendStatus sendEmail(List mailTos, List mailCcs, String subject, String content,
                                           String personal, List attachments, String user, String pwd) {
        if (StringUtils.isEmpty(content)) {
            return MailSendStatus.CONTENT_EMPTY;
        }
        if (StringUtils.isEmpty(user) || StringUtils.isEmpty(pwd)) {
            return MailSendStatus.USER_OR_PWD_EMPTY;
        }

        String[] to = parseAddr(mailTos);
        if (null == to) {
            return MailSendStatus.RECEIVER_EMPTY;
        }

        // 邮件发送器参数设置
        JavaMailSenderImpl senderParam = new JavaMailSenderImpl();
        senderParam.setHost("邮箱 smtp host 地址");
        senderParam.setUsername(user);
        senderParam.setPassword(pwd);
        Properties javaMailProperties = new Properties();
        javaMailProperties.put("mail.smtp.timeout", "超时时间");
        javaMailProperties.put("mail.smtp.connectiontimeout", "链接超时时间");
        senderParam.setJavaMailProperties(javaMailProperties);

        try {
            MimeMessageHelper helper = new MimeMessageHelper(senderParam.createMimeMessage(), true, "UTF-8");
            // 邮件发送人
            helper.setFrom(senderParam.getUsername(),
                    StringUtils.isEmpty(personal) ? "默认发件人显示名" : personal);
            // 邮件接收人
            helper.setTo(to);
            // 抄送邮件
            String[] cc = parseAddr(mailCcs);
            if (null != cc) {
                helper.setCc(cc);
            }
            // 邮件主题
            helper.setSubject(StringUtils.isEmpty(subject) ? "默认主题名称" : subject);
            // 邮件内容
            helper.setText(buildContent(content), true);
            // 添加附件
            if (null != attachments && attachments.size() > 0) {
                for(File file : attachments){
                    helper.addAttachment(MimeUtility.encodeText(file.getName()), file);
                }
            }
            // 发送时间
            helper.setSentDate(new Date());

            // 邮件发送
            Transport transport = helper.getMimeMessage().getSession().getTransport();
            // 注册一个监听器，当有无效邮件地址异常时，我们将有效的且未发送的邮件地址重新投递
            transport.addTransportListener(new TransportAdapter() {
                @Override
                public void messageNotDelivered(TransportEvent event) {
                    // 获取到有效的且未发送的邮件地址
                    Address[] validAddresses = event.getValidUnsentAddresses();
                    if (null == validAddresses || validAddresses.length == 0) {
                        return;
                    }
                    // 获取发送内容信息
                    Message message = event.getMessage();
                    try {
                        // 重新发送
                        transport.sendMessage(message, validAddresses);
                    } catch (Exception ex) {
                        log.error("mail send failed", ex);
                    }
                }
            });
            transport.connect(senderParam.getHost(), senderParam.getUsername(), senderParam.getPassword());
            transport.sendMessage(helper.getMimeMessage(), helper.getMimeMessage().getAllRecipients());

            return MailSendStatus.SUCCESS;
        } catch (SendFailedException ex) {
            log.error("邮件发送地址无效: {}", Arrays.toString(ex.getInvalidAddresses()));
            return MailSendStatus.PART_SUCCESS;
        } catch (MessagingException ex) {
            log.error("邮件发送初始化异常", ex);
        } catch (UnsupportedEncodingException ex) {
            log.error("邮件编码异常", ex);
        } catch (Exception ex) {
            log.error("邮件发送异常", ex);
        }

        return MailSendStatus.FAIL;
    }
}

public enum MailSendStatus {
    SUCCESS("发送成功"),
    FAIL("发送失败"),
    PART_SUCCESS("部分成功"),
    CONTENT_EMPTY("邮件内容为空"),
    RECEIVER_EMPTY("邮件接收人为空"),
    USER_OR_PWD_EMPTY("用户名或密码为空")
    ;

    @Getter
    private String desc;

    MailSendStatus(String desc) {
        this.desc = desc;
    }
}

原理

请打开 com.sun.mail.smtp.SMTPTransport#rcptTo() 方法

public class SMTPTransport extends Transport {

    ...

    protected void rcptTo() throws MessagingException {

    ...

        // try the addresses one at a time
        for (int i = 0; i < addresses.length; i++) {

            ...

            // check the server's response for address validity
            // 如果是失效地址，retCode 为550
            retCode = readServerResponse();

            ...

        }

            ...

         // copy the lists into appropriate arrays
        // 将无效的邮件地址放入 Address[] validUnsentAddr 中
        if (sendFailed) {
            // copy invalid addrs
            invalidAddr = new Address[invalid.size()];
            invalid.toArray(invalidAddr);

            // copy all valid addresses to validUnsent, since something failed
            validUnsentAddr = new Address[valid.size() + validUnsent.size()];
            int i = 0;
            for (int j = 0; j < valid.size(); j++)
              validUnsentAddr[i++] = (Address)valid.get(j);
            for (int j = 0; j < validUnsent.size(); j++)
              validUnsentAddr[i++] = (Address)validUnsent.get(j);
        }

        ...

        // 通知监听器
        notifyTransportListeners(TransportEvent.MESSAGE_NOT_DELIVERED,
                     validSentAddr, validUnsentAddr,
                     invalidAddr, this.message);
        ...

    }

    ...

}