JavaMail 发送附件不成功，为何？

[startsun]

MimeBodyPart mbp2=new MimeBodyPart();

File file = new File(filename);
FileDataSource fds=new FileDataSource(file);

mbp2.setDataHandler(new DataHandler(fds));
mbp2.setFileName(fds.getName());


mp.addBodyPart(mbp2);



// 把MultiPart加入邮件
msg.setContent(mp);