This sounds like great fun!
I know there are people such as are found at http://www.postcardpolaroid.com/ that shoot a polaroid usually of the SX70 variety, address it, bung a stamp on it, post it and it gets where it should.

The Polaroid company used to have sticky Postcard backings called "Postcarders" to stick your Polaroid prints on. They were 3.1" x 4.1" in size. I used to shoot some travel photos with the Model 800 camera and send a postcard to friends or family. Easy, simple and fun. UNTIL, about 1980ish the folks at the U.S. Post office informed me it could NOT accept these as they DO NOT meet minimum size for postcards.

The Post office regulation SAYS: Minimum Allowable Postcard Size: 3.5 x 5 Inches
If the width is less than 5 inches or the height is less than 3.5 inches the USPS will NOT mail your postcard.

I miss my polaroid postcards!!!! THEN I read about these folks at postcardpolaroid.com sending a SX70 type polaroid through the mail WITHOUT a backing, just a stamped, addressed, naked polaroid. They say on the site that they get to the people they are sent to. SO I send a SX70 stamped and addressed print to my family in Minneapolis from Maryland. I fly out to visit and await the postcard for 10 days, NO postcard. I then send a SX70 postcard from Minneapolis to Maryland. I then fly back home to Maryland. It has been two weeks since I sent the Polaroid postcard. NO postcard has arrive either here in Maryland nor Minneapolis.

So am I missing something?? How is this going to work? I'd like it to work so I could once again send Polaroid post cards reliably to people.

The only way I've been able to send a Polaroid via postcard , is to make a custom backer with a decorative border and inset the polaroid photo so that the surface of the Polaroid print was flush with the surface of the surrounding border. THE REASON was the post office did not like the Polaroid print just "Stuck" on the card with its raised surface being higher by .008" than the backing.

Some things just gotta be hard and complicated!

Let me know what you know,
Sam H.