无法连接到SMTP主机：xxxx，端口：java中的25

Question

I cannot send email in Java, it throw Exception: Could not connect to SMTP host: xxxx, port: 25.

I telnet xxxx 25 OK and I sent email successfully in php code with the same host, port, user & password, so I don't think this issue due to network or firewall problems.

In testing, I sent email OK in java with gmail server (smtp.gmail.com :465), but not with host: xxxx port 25.

This is my java code: HOST=xxxx

Properties mailServerProperties = System.getProperties();
mailServerProperties.put("mail.smtp.user", USER);
mailServerProperties.put("mail.smtp.host", HOST);
mailServerProperties.put("mail.smtp.port", 25);
mailServerProperties.put("mail.smtp.debug", "true");
mailServerProperties.put("mail.smtp.auth", "true");
mailServerProperties.put("mail.smtp.starttls.enable", "true");
mailServerProperties.put("mail.smtp.socketFactory.port", 25);
mailServerProperties.put("mail.smtp.socketFactory.class", "javax.net.ssl.SSLSocketFactory");

javax.mail.Session getMailSession = javax.mail.Session.getDefaultInstance(mailServerProperties);
MimeMessage generateMailMessage = new MimeMessage(getMailSession);
generateMailMessage.setHeader("Content-Type", "text/plain; charset=UTF-8");
generateMailMessage.setSubject(subject, "UTF-8");
generateMailMessage.setFrom(new InternetAddress(ApiConstant.EMAIL, fromEmail, "UTF-8"));
generateMailMessage.addRecipients(Message.RecipientType.TO, toAddress);
generateMailMessage.addRecipients(Message.RecipientType.CC, ccAddress);
generateMailMessage.addRecipients(Message.RecipientType.BCC, bccAddress);

Multipart multipart = new MimeMultipart();
MimeBodyPart messagePart = new MimeBodyPart();
messagePart.setContent(content, "text/html; charset=UTF-8");
multipart.addBodyPart(messagePart);       
generateMailMessage.setContent(multipart);

logger.debug("Create transport");
Transport transport = getMailSession.getTransport("smtp");
transport.connect(HOST, 25, USER, PASS);
transport.sendMessage(generateMailMessage, generateMailMessage.getAllRecipients());
transport.close();

This is my php code, it worked.

$mail = new PHPMailer();
$mail->Host = 'x.x.x.x';
$mail->Port = '25';
$mail->SMTPAuth = true;
$mail->Username = USER;
$mail->Password = PASS;
$mail->From = '.....';
$mail->FromName = '.....';

$mail->setLanguage('vi');
$mail->isHTML(true);
$mail->CharSet = 'UTF-8';
$mail->addAttachment(FILE_NAME);
$mail->addAddress('....');
$mail->Subject ="test";
$mail->Body = "test";
$mail->Body = $body;

Plz help me.

Answer 1

On some networks, IPv6 may be problematic. Try running your app with the VM option

-Djava.net.preferIPv4Stack=true

ie

java -Djava.net.preferIPv4Stack=true -cp . MyClass