Jeezit, Homestar. Where do you live? Utah? Why's everybody always hiding the mail from their children?
Tell your parents that if they're too cold and apathetic to take the time to understand their child's hobby, then you're just gonna go get new parents,
I'm kidding. I'm sure your parents are nice caring people - that's why they're trying to protect you after all. On the other hand, I does irk me when parents give an unthinking knee-jerk, "No," to anything they don't understand. Just because it's somthing they never did as a kid doesn't mean it's a waste of time. Man, if some intelligent adult were to just explain to them why Magic is such a good hobby for kids, they'd probably be jumping at the chance to encourage you.
PS - While I feel your parents are being foolish for not letting you recieve a bunch of free magic cards in the mail, I would like to suggest that you do NOT just give out the address without telling your parents. Don't break their trust - you'll regret it for a long time if you do.