I just took a look at it. according to the usps website it looks like yo do have to label your postcards with a city, state, address, and a code, and I was under the impression you have to fill out a form, get a permit, do the carrier route codes, etc. also, I am not sure about the size. it looks like you have to have a minimum size that is larger than the current cards I use. Have you used this before? I'd like more info. this sounds awesome.