You may want to check this website.
http://www.ece.cmu.edu/prospective/graduate/decision/
Use the email account and password you created when applying. Good luck!
Seems that all decisions were sent out in snail mail last year, according to the results posted. Well, I can't really understand that, why not notify via email first? It's pretty risky to send such important docs by surface mail, easily get lost especially international ones.