Actually the email header gives no clue if it is acceptance or what. And then you open it and it has a little blurb. My admission email had a letter attached to it, they don't actually ever snail mail you anything, even once you accept your spot, you have a website that you can access everything through. =)
I think that they have somewhere between 20-30 on the waitlist, last year they overaccepted 10. So you have to wait for 10 people to decline before they pull from the waitlist.
You can call the admin office and they will tell you your position # and give you an idea of how deep into the waitlist they usually go. If I remember right they said anywhere from 6-18 people is their average....But of course each year is different.