I did the same as you.
But I also posted a global announcement in which I explain the problem. I put a link to that announcement in the line on the register page where email is explained.
I even made a small guide, on a html-page, with some images, in which I explain how to configure Hotmail junkfilter. In the announcement there´s a link to that guide.
Some people must end up dizzy before ever getting to register.
But I believe all this could help a bit.
