It's one of the latest social engineering exploits: an updated version of the "Storm" trojan. The YouTube link is bogus, you actually get taken to some cracked machine with a cheesy mockup of YouTube. On that page is a link to download a file called "video.exe", which is the exploit program. If you are inferring that the sending host is Exim/FreeBSD based on the headers of the message, then that's probably a mistake because those are almost certainly forged.
