Java类连接Gmail SMTP发送邮件认证失败，账号密码可正常登录

问题背景 #

创建Gmail账号unreal@gmail.com（密码q1234567），使用Java代码发送邮件时触发AuthenticationFailedException，提示用户名密码不被接受，但网页端可正常登录。

发送邮件代码 #

public void sendMail() {
    String d_email = "unreal@gmail.com",
            d_uname = "unreal@gmail.com",
            d_password = "q1234567",
            d_host = "smtp.gmail.com",
            d_port = "465",
            m_to = "dummy_38@hotmail.com",
            m_subject = "Indoors Readable File: ",
            m_text = "This message is from Indoor Positioning App. Required file(s) are attached.";
    Properties props = new Properties();
    props.put("mail.smtp.user", d_email);
    props.put("mail.smtp.host", d_host);
    props.put("mail.smtp.port", d_port);
    props.put("mail.smtp.starttls.enable", "true");
    props.put("mail.smtp.debug", "true");
    props.put("mail.smtp.auth", "true");
    props.put("mail.smtp.socketFactory.port", d_port);
    props.put("mail.smtp.socketFactory.class", "javax.net.ssl.SSLSocketFactory");
    props.put("mail.smtp.socketFactory.fallback", "false");

    Session session = Session.getInstance(props,
            new javax.mail.Authenticator() {
                protected PasswordAuthentication getPasswordAuthentication() {
                    return new PasswordAuthentication(username, password);
                }
            });


    session.setDebug(true);

    MimeMessage msg = new MimeMessage(session);
    try {
        msg.setSubject(m_subject);
        msg.setFrom(new InternetAddress(d_email));
        msg.addRecipient(Message.RecipientType.TO, new InternetAddress(m_to));

        Transport transport = session.getTransport("smtps");
        transport.connect(d_host, Integer.valueOf(d_port), d_uname, d_password);
        transport.sendMessage(msg, msg.getAllRecipients());
        transport.close();

    } catch (AddressException e) {
        e.printStackTrace();

    } catch (MessagingException e) {
        e.printStackTrace();

    }

}

报错日志片段 #

DEBUG SMTP: protocolConnect login, host=smtp.gmail.com, user=unreal@gmail.comm, password=<non-null>
DEBUG SMTP: AUTH LOGIN failed
javax.mail.AuthenticationFailedException: 535-5.7.8 Username and Password not accepted.

解决步骤 #

1. 修复代码变量引用错误 #

从日志能看到登录用户名变成了unreal@gmail.comm（多了一个m），原因是匿名Authenticator类中使用了未定义的username和password变量，替换为代码中声明的d_uname和d_password：

Session session = Session.getInstance(props,
        new javax.mail.Authenticator() {
            protected PasswordAuthentication getPasswordAuthentication() {
                return new PasswordAuthentication(d_uname, d_password);
            }
        });

2. 启用应用专用密码（核心解决方法） #

Gmail已禁用普通密码的SMTP登录，即使网页端能登录也无法直接使用账号密码发邮件：

• 先为账号开启两步验证（必须前置操作）
• 进入Google账号管理页面，生成应用专用密码
• 将代码中的d_password替换为生成的应用专用密码

3. 简化SMTP配置参数 #

端口465为SSL端口，可简化配置，移除冗余的socketFactory相关属性：

Properties props = new Properties();
props.put("mail.smtp.host", d_host);
props.put("mail.smtp.port", d_port);
props.put("mail.smtp.auth", "true");
props.put("mail.smtp.ssl.enable", "true");
props.put("mail.smtp.debug", "true");

4. 排查账号安全状态 #

• 检查账号最近登录记录，确认是否有异常登录被拦截
• 确保未开启账号的异常安全限制

内容的提问来源于stack exchange，提问作者user1999453