JavaMail API附件不能是multipart的最后记录

I am using javamail api to develop my android app to send a mail with attachment. However, I discover that if the attachment is the last record of the multipart, then the mail cannot be delivered to the destination. I have no idea why this happen, and I have search there does not have similar question discussing on this issue. So I open this question and would like to seek answer from experts here.I am using javamail api to develop my android a