I always enjoy reading TBN threads when it comes to US mailboxes. Especially when it comes to your standardisation of the boxes themselves and the conformity of the regulations that must be adhered to.
The following are pictures of actual (and very typical) Australian rural mailboxes. Those that are an old oil drum (even the plastic ones) have a rock in them so that the Postie can put it on top of your letters so they wont blow away. And, yes, that last one is an old microwave oven... very popular (as long as the door still works :laughing
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Feel free to GIS Australian Mailboxes for more examples.