通过 JavaMail 发送到 Gmail 时的 TLS 问题

事实证明，JavaMail 比我想象的要令人沮丧一些。我在网上查看了几个有关如何通过 Gmail 服务器（但不通过 SSL）发送简单 SMTP 电子邮件的示例。在尝试了几个不同的代码示例之后，当我调用时，我不断得出相同的示例异常transport.connect()。我不断收到这个堆栈跟踪：

Exception in thread "main" com.sun.mail.smtp.SMTPSendFailedException: 530 5.7.0 Must issue a STARTTLS command first. l10sm302158wfk.21
     at com.sun.mail.smtp.SMTPTransport.issueSendCommand(SMTPTransport.java:2057)
     at com.sun.mail.smtp.SMTPTransport.mailFrom(SMTPTransport.java:1580)
     at com.sun.mail.smtp.SMTPTransport.sendMessage(SMTPTransport.java:1097)
     at SendEmail.main(SendEmail.java:47)

有人可以告诉我应该添加什么或做什么来解决这个问题吗？

这是我的代码：

    Properties props = new Properties();
    props.put("mail.transport.protocol", "smtp");
    props.put("mail.host", "smtp.gmail.com");
    props.put("mail.user", "[email protected] /cdn-cgi/l/email-protection");
    props.put("mail.password", "blah");
    props.put("mail.port", "587");

    Session mailSession = Session.getDefaultInstance(props, null);
    Transport transport = mailSession.getTransport();

    MimeMessage message = new MimeMessage(mailSession);
    message.setSubject("This is a test");
    message.setContent("This is a test", "text/plain");
    message.addRecipient(Message.RecipientType.TO, new InternetAddress("[email protected] /cdn-cgi/l/email-protection"));

    transport.connect();
    transport.sendMessage(message, message.getRecipients(Message.RecipientType.TO));
    transport.close();

您需要启用STARTTLS。在您的配置中再添加一项属性：

props.put("mail.smtp.starttls.enable", "true");