hotmail has some strange issue with headers in a message. I am still investigating this, and have devoted many hours to trying to nail it down.
something I have come up with however, is if you use gmail, and receive a message, then go to the "more options" link in the email, and then "show original", it pops up a window with the email content (including all headers etc). If you cut this, and paste it into a telnetted SMTP conversation to hotmail's servers, the message gets through.
It's something I am REALLY trying to figure out.
I'll do my best to keep you posted.