Unfortunately, if the USPS person wants that package to fit into the mailbox, "DO NOT BEND" or a cardboard backer is not going to stop it.
On a personal level, I am very lucky as any package I order of discs to my own home my USPS carrier will deliver it right to my door instead of trying to cram it into my mailbox and moving on....
That's what I thought.
I've ordered lots of discs from many different sources, including rdg, and I've never had damage due to the USPS.
Luckily they only have the option of leaving them on my front porch.