knee mail

例句：

1. 1. I received a knee mail from my friend last week.
   我上周收到了朋友的膝盖邮件。
2. 2. He sent me a knee mail with his latest research findings.
   他给我寄来了一份带有最新研究成果的膝盖邮件。
3. 3. The sender of the knee mail was not identified.
   膝盖邮件的发送者尚未确认。