使用JAVAMAIL对MESSAGE进行操作时的问题

[chenyun2000]

public void removePart(int msgnum, int partnum)
throws MailException
{
try {
if (msgnum>messageCount || msgnum<=0)
throw new MailException(labels.getString("1025"));

Message msg=m_folder.getMessage(msgnum);
Multipart mp = (Multipart) msg.getContent();

if (partnum<0 || partnum>mp.getCount())
throw new MailException(labels.getString("1028"));

mp.removeBodyPart(partnum); //出错在此处
msg.setContent(mp);
msg.setSentDate(new java.util.Date());
msg.saveChanges();
} catch (Exception ex) {
throw new MailException(ex.getMessage());
}

}

错误提示如下：
IMAPMessage is read-only

如何解决？请高手指教。谢了！

[chenyun2000]

高手在那？急救！