Tony M sends my circles back

I have been placing postcards inside most of the envelopes I send out to give them some weight.

Looks like I forgot to write anything on this one I sent to Tony, so he wrote the address on the front. I like how he used one of the circles to center his return address stamp.

Then he put his message on the back. This is another piece of mail art with postage divided between the front and back - not sure that would be allowed by the USPS, maybe it's time for a post office test.