You should bake it fairly dense or it will most likely arrive in crumbs. Marking it Fragile won't be enough. I would use one of those half gallon size ziplock bags.

Can you pack it in styrofoam peanuts? Or, real popcorn would work, to help cushion it.

I think 2 day shipping would be OK. You could bake it, let it cool completely, then wrap it in waxed paper first followed by foil. Put the cornbread in the box which you've half-filled with peanuts or popcorn, and then fill it up the rest of the way with more popcorn.

That must be some great cornbread if you're willing to go to the trouble to ship it.

I'd put it into a disposable (e.g. Glad) plastic food container and ship it priority mail, in one of those flat-rate boxes. They normally arrive within 2 days for me.
Put lots of expanded polystyrene, or bubble wrap around the container. Pad the cornbread within with something like scrunched up greaseproof paper, to stop it tumbling around.
And yes, I'd like to try that cornbread, if it is worth shipping ... :-)

If you can cook it in a foil container that may help it arrive intact.
(Assuming you mean the risen type cornbread and not the flat, bacon grease+cornmeal 'n water type of cornbread I grew up eating and love the best)

Cornbread *whimper* These heathen Canadians up here don't know what they're missing AND I DO! *whimper*

My grandmother in Colorado used to send cookies and other baked goods to me in Alaska. The only problem was that very moist things like banana bread could/would get moldy, but she also wasn't using priority mail and she lived in a very rural area so it would take a while to get here.

My mother has sent me corn bread from Washington (state) and while it got here quickly enough it does have the tendency to crumble in shipping.

Put it into a tin! That's what tins are for. Then put it in a box, and pack carefully around the tin with newspaper so it can't shift in the box.

This is a derail but you will thank me:

Once while I was visiting a friend in Southern California, the mail arrived. There was this brown paper bag, and it had been folded up, taped, stamped and addressed. It had also gotten pretty greasy. Very greasy. Inside was alligator meat that a friend in Louisiana had mailed to my So Cal friend.

I would not recommend sending cornbread that way, though.

Add a bunch of styrofoam packing peanuts to the actual corn bread mix.

If you can cook it in a foil container that may help it arrive intact.

Or you could wrap it the way I wrap baked goods for travel*:
- from a cereal box (or whatever's handy), cut a piece of lightweight cardboard the same size as the cornbread
- wrap the cardboard in foil
- place the cornbread on the foil-wrapped cardboard
- wrap the whole thing tightly in plastic wrap or foil

Then you can put it in a tin or Gladware or whatever other container. Being wrapped snugly onto a nice sturdy base makes it a little less prone to splitting into chunks. If the tin or container isn't a snug fit, fill it as suggested above: with packing peanuts, with crumpled parchment, or with air-popped popcorn. You don't want it bouncing against the container walls.

One other tactic I use: when baked goods are traveling any distance, I often bake them in smaller pans. Small cakes/quick breads and muffins seem to me to hold up better than big flat loaves.

*When I say "travel," I just mean "bouncing around in a cooler or bag in the bed of the pick-up truck; I very rarely mail food. But I can't remember anything wrapped this way ever breaking apart, even after a few hours' bouncy drive.

Cornbread...buttery cornbread...cornbread....may I never live in a place where it has to be mailed to me! Cornbread is the perfect comfort food. Not only does it taste like nothing else does, but it settles your stomach and calms your mood like few other foods do.