Outlook Express Mail sent.. want to get it back…

I am using outlook express 2003. I have mistakenly send a message to my boss. Which I had to send to my friend. I want this mail to be fetched back. And my boss can not see its content. The PC of my boss on which his mail box is configured is powered off write now. Please give me any solution so that I may not get caught in any problem. Please help immediately.
