无法连接到SMTP主机.Java邮件错误

Question

我正在尝试使用java邮件API发送邮件。这是我的代码

 public static void sendMail(MailObject mail) throws Exception
       {    

          String to = mail.toAdress;
          String from = mail.fromName;        
          String host = "mail.mycompanyname.com"; //$NON-NLS-1$
        //  String port="25";
          Properties properties = System.getProperties();        
          properties.setProperty("mail.smtp.host", host); //$NON-NLS-1$
        // properties.setProperty()); //$NON-NLS-1$ //$NON-NLS-2$
          properties.put("mail.smtp.port", "25");
          Session session = Session.getDefaultInstance(properties);

           //  MimeMessage message = new MimeMessage(session);

            String add = mail.attachmentLocation;

             MimeMessage message = new MimeMessage(session);
             message.setSubject(mail.subject);
              // create the message 
              MimeBodyPart messageBodyPart = new MimeBodyPart();

              //fill message to be sent
              messageBodyPart.setText(mail.message);

              Multipart multipart = new MimeMultipart();
              multipart.addBodyPart(messageBodyPart);

              //attach your file here
              messageBodyPart = new MimeBodyPart();

              DataSource source =  new FileDataSource(mail.attachmentLocation); // your file
              messageBodyPart.setDataHandler( new DataHandler(source));
              messageBodyPart.setFileName(mail.attachmentName);
              multipart.addBodyPart(messageBodyPart);

              // Put message in parts
              message.setContent(multipart);

             message.setFrom(new InternetAddress(from));

             message.addRecipient(Message.RecipientType.TO,
                                      new InternetAddress(to));




             Transport.send(message);
             System.out.println("Sent message successfully...."); //$NON-NLS-1$

       }
class MailObject
{
String toAdress;
String fromName;
String subject;
String message;
String attachmentLocation;
String attachmentName;
HTMLPage pageObject;
}

但我得到无法连接到smtp服务器错误。这是完整的堆栈跟踪

javax.mail.MessagingException: Could not connect to SMTP host: mail.mycompany.com, port: 25;
  nested exception is:
    java.net.SocketException: Network is unreachable: connect
Could not connect to SMTP host: mail.mycompanyname.com, port: 25
    at com.sun.mail.smtp.SMTPTransport.openServer(SMTPTransport.java:1282)
    at com.sun.mail.smtp.SMTPTransport.protocolConnect(SMTPTransport.java:370)
    at javax.mail.Service.connect(Service.java:275)
    at javax.mail.Service.connect(Service.java:156)
    at javax.mail.Service.connect(Service.java:105)
    at javax.mail.Transport.send0(Transport.java:168)
    at javax.mail.Transport.send(Transport.java:98)
    at MailManager.sendMail(MailManager.java:68)
    at MailManager$1.widgetSelected(MailManager.java:122)
    at org.eclipse.swt.widgets.TypedListener.handleEvent(Unknown Source)
    at org.eclipse.swt.widgets.EventTable.sendEvent(Unknown Source)
    at org.eclipse.swt.widgets.Display.sendEvent(Unknown Source)
    at org.eclipse.swt.widgets.Widget.sendEvent(Unknown Source)
    at org.eclipse.swt.widgets.Display.runDeferredEvents(Unknown Source)
    at org.eclipse.swt.widgets.Display.readAndDispatch(Unknown Source)
    at MailManager.openMailDialogue(MailManager.java:165)
    at App2$2.widgetSelected(App2.java:311)
    at org.eclipse.swt.widgets.TypedListener.handleEvent(Unknown Source)
    at org.eclipse.swt.widgets.EventTable.sendEvent(Unknown Source)
    at org.eclipse.swt.widgets.Display.sendEvent(Unknown Source)
    at org.eclipse.swt.widgets.Widget.sendEvent(Unknown Source)
    at org.eclipse.swt.widgets.Display.runDeferredEvents(Unknown Source)
    at org.eclipse.swt.widgets.Display.readAndDispatch(Unknown Source)
    at App2.main(App2.java:521)
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:232)
    at com.sun.mail.util.SocketFetcher.getSocket(SocketFetcher.java:189)
    at com.sun.mail.smtp.SMTPTransport.openServer(SMTPTransport.java:1250)
    ... 23 more

我尝试使用telnet ping服务器，它显示了欢迎屏幕。