I just wanted to upload a pic to have an example for how I package things.

Firstly, I have all artwork you buy is put in a large bubblewrap lined envelope (i don't fold any artwork)
Next, I add a peice of corrugated cardboard to deter any postman from trying to fold it
Then, I write "DO NOT BEND" on both sides, hopefully to prevent any postman thinking its ok to cram it in a mailbox by folding it.
And last of course, add stamps and your address

I know how much it sucks to get a damaged/folded up peice of artwork in the mail! It pretty much makes it unframeable and generally unpresentable. I take these extra measures to make sure that your artwork from me arrives safely and undamaged.
Allthough that is also deemed to be weather permitting, so hopefully it doesn't get caught in the rain! Hopefully the bubblewrap lining of the envelope is at least a little bit water resistant ;)

Also!
Lamination of artwork is available too! I use a thermal lamination method that makes your artwork super tough, about half as thick as a credit card and completely waterproof.