When I first saw these I was instantly intrigued. 1- because who doesn't love getting Happy Mail and 2 - it incorporates ATC's which I have always enjoyed making.
This was my first attempt at making one earlier this year. I admit that it was not my greatest work, but you have to start somewhere, so I started. I made my 9 little ATC's in a vintage theme and then added some little goodies to the back and when I was ready to send it off to my swapping buddy then I made a little dangle charm to hang off the edge and personalize it a bit more.