Good idea except that with today's technology, not too many people are still going to want to use the mail if it isn't going to give them some kind of return other than just 'some other guy' hearing your music.
It's easier to design a web page with a biography and press package. Then add some lo-fi and hi-fi MP3's with examples of your best work. Those who want to have an actual CD can contact you and make arrangements through your web page for a promotional copy or they can choose to buy your CD or files right off your site.
Trading a CD by mail only gets your music out to a very few people. Having a website can get you thousands of hits a week from around the world if you promote it right.