javamail,为什么folder返回总是为0？？

Question

inbox.open(Folder.READ_ONLY);
      if(inbox.isOpen()){System.out.println("inbox Folder is Open");}
      messageCount=inbox.getMessageCount();
      noReadNum=inbox.getUnreadMessageCount();
      Message msgs[]=inbox.getMessages();
      System.out.println("msgs.length="+msgs.length);
      System.out.println("noReadNum="+noReadNum+"messageCount="+messageCount);以上为代码片断，noReadNum和messageCount均为0，确信邮箱里肯定有信件！！！