发送邮件：java.net.SocketException：网络无法访问：连接

尝试通过javax.mail发送邮件：

Properties props = new Properties(); props.put("mail.smtp.host", "xxxxx"); props.put("mail.smtp.port", "25"); props.put("mail.smtp.auth", "false"); Session session = Session.getInstance(props, new javax.mail.Authenticator() { protected PasswordAuthentication getPasswordAuthentication() { return new PasswordAuthentication("xx", "xx"); } }); try { Message message = new MimeMessage(session); message.setFrom(new InternetAddress("xxxxx")); message.setRecipients(Message.RecipientType.TO, InternetAddress.parse("xxxxx")); message.setSubject("Subject"); message.setText("Body"); Transport.send(message); System.out.println("Done"); } catch (MessagingException e) { throw new RuntimeException(e); } 

它抛出exception

 Exception in thread "main" java.lang.RuntimeException: javax.mail.MessagingException: Could not connect to SMTP host: srv-mail.imb.invention.com, port: 25; nested exception is: java.net.SocketException: Network is unreachable: connect at foo.SendMailTest.main(SendMailTest.java:41) Caused by: javax.mail.MessagingException: Could not connect to SMTP host: xxx.xxxx.zzzzz.com, port: 25; nested exception is: java.net.SocketException: Network is unreachable: 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:295) at javax.mail.Service.connect(Service.java:176) at javax.mail.Service.connect(Service.java:125) at javax.mail.Transport.send0(Transport.java:194) at javax.mail.Transport.send(Transport.java:124) at foo.SendMailTest.main(SendMailTest.java:36) Caused by: java.net.SocketException: Network is unreachable: connect at java.net.DualStackPlainSocketImpl.connect0(Native Method) at java.net.DualStackPlainSocketImpl.socketConnect(Unknown Source) at java.net.AbstractPlainSocketImpl.doConnect(Unknown Source) at java.net.AbstractPlainSocketImpl.connectToAddress(Unknown Source) at java.net.AbstractPlainSocketImpl.connect(Unknown Source) at java.net.PlainSocketImpl.connect(Unknown Source) at java.net.SocksSocketImpl.connect(Unknown Source) at java.net.Socket.connect(Unknown Source) at java.net.Socket.connect(Unknown Source) at com.sun.mail.util.SocketFetcher.createSocket(SocketFetcher.java:321) at com.sun.mail.util.SocketFetcher.getSocket(SocketFetcher.java:237) at com.sun.mail.smtp.SMTPTransport.openServer(SMTPTransport.java:1927) ... 7 more 

服务器可用：

 C:\work\test>nc.exe xxx 25 220 xxx.zzz.aaaaaaa.com Microsoft ESMTP MAIL Service ready at Thu, 12 Sep 2013 15:10:45 +0300 

ping也行。

类似的.net代码按预期工作。

我不知道出了什么问题……

Answer 1

答案是：java更喜欢IPv6，但在我们公司中它有问题。 添加属性java.net.preferIPv4Stack=true可以解决问题。