Go to http://www.completewhois.com/rbl_lookup.htm and enter your server's IP address. It could be that your server's IP or netblock was blacklisted for spam. Hotmail may now be junking mail from your domain because it was coming from known spam IPs.
Matt Bloom AngryHosting - Load balanced/redundant shared hosting solutions
(Funny thing: when I clicked Submit, there was a message saying that a response should be sent to me within 24 hours.. If no response was received, it said that I should check my Junk mail folder !! lol )
I will update this post if I ever receive a response from Hotmail !