java - SMTP TLS 不适用于 gmail

Question

我想编写一个使用 SMTP TLS 连接到 gmail 服务器的程序。我正在使用此页面上提到的代码:

http://www.mkyong.com/java/javamail-api-sending-email-via-gmail-smtp-example/

我收到连接超时异常。如果我使用 SMTP SSL，我可以成功发送电子邮件。

public void sendUsingSMTP_TLS() {
    final String username = "username@gmail.com";
    final String password = "password";

    Properties props = new Properties();
    props.put("mail.smtp.auth", "true");
    props.put("mail.smtp.starttls.enable", "true");
    props.put("mail.smtp.host", "smtp.gmail.com");
    props.put("mail.smtp.port", "587");

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

    try {

        Message message = new MimeMessage(session);
        message.setFrom(new InternetAddress("from-email@gmail.com"));
        message.setRecipients(Message.RecipientType.TO,
            InternetAddress.parse("to-email@gmail.com"));
        message.setSubject("Testing Subject");
        message.setText("Dear Mail Crawler,"
            + "\n\n No spam to my email, please!");

        Transport.send(message);

        System.out.println("Done");

    } catch (MessagingException e) {
        throw new RuntimeException(e);
    }
}

我得到以下异常:

 Exception in thread “main” java.lang.RuntimeException: javax.mail.MessagingException:              
Could not connect to SMTP host: smtp.gmail.com, port: 587;
nested exception is:
java.net.ConnectException: Connection timed out: connect
at SMTP_TLS.main(SMTP_TLS.java:48)
Caused by: javax.mail.MessagingException: Could not connect to SMTP host: smtp.gmail.com, port: 587;
nested exception is:
java.net.ConnectException: Connection timed out: connect
at com.sun.mail.smtp.SMTPTransport.openServer(SMTPTransport.java:1961)
at com.sun.mail.smtp.SMTPTransport.protocolConnect(SMTPTransport.java:654)
at javax.mail.Service.connect(Service.java:317)
at javax.mail.Service.connect(Service.java:176)
at javax.mail.Service.connect(Service.java:125)
at javax.mail.Transport.send0(Transport.java:253)
at javax.mail.Transport.send(Transport.java:124)
at SMTP_TLS.main(SMTP_TLS.java:43)
Caused by: java.net.ConnectException: Connection timed out: connect
at java.net.DualStackPlainSocketImpl.connect0(Native Method)
at java.net.DualStackPlainSocketImpl.socketConnect(DualStackPlainSocketImpl.java:69)
at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:339)
at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:200)
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:182)
at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:157)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:391)
at java.net.Socket.connect(Socket.java:579)
at java.net.Socket.connect(Socket.java:528)
at com.sun.mail.util.SocketFetcher.createSocket(SocketFetcher.java:299)
at com.sun.mail.util.SocketFetcher.getSocket(SocketFetcher.java:234)
at com.sun.mail.smtp.SMTPTransport.openServer(SMTPTransport.java:1927)
… 7 more

Answer 1

异常意味着您无法连接到服务器 smtp.gmail.com 上的端口 587。使用 telnet 验证这一点:

telnet smtp.gmail.com 587

(这对我有用，所以服务器和端口号是正确的。)

这在您所在的位置不起作用的可能原因是:

• Java 中错误配置的代理设置
• 您所在位置的防火墙禁止连接到此端口号。

如果上面的 telnet 命令可以连接，则可以排除防火墙的问题。但如果它不起作用并且您在公司网络中，则很可能是防火墙导致了问题。

此外，找出用于其他连接方法的端口号。也许这也适用于 TLS。