Aha! “Federal Property” explained, sort of;
simple
They don’t actually want your custom, hard-earned mailbox. They just want juristiction so they can go after the baddies who would mess with it.
Postal Inspectors. {{{My heros}}}. 
Peace,
mangeorge
OK, let me correct something I posted earlier. Strictly speaking, the U.S. Postal Service does not own your mailbox. They cannot take possession of it, or dispose of it. They do, however, have sole claim to the usage of whatever recepticle you put out for the USPS to deliver your mail. Whatever you put out must be used for USPS mail deliver alone, with no other usage.
That is why the section of the U.S. Code that I quoted above is careful to say “any property used by the Postal Service.”
**
Okay, straight from the horse’s mouth–the Better Half, on his way to bed, is cornered and Attrayant’s post read to him. He replies:
I ask, “Just by the act of putting it on your porch?”
He says, “Yes. You buy it, maintain it, and own it, but the USPS has exclusive dibs on putting stuff like mail and flyers in it.”
He adds that this is all covered by something called the “private express statutes”, which when looked up on Google proved to be such a morass of PDF files that we both gave up trying to find the relevant statute.
So.
I will also say that we, personally, frequently tell people to drop stuff off at our house by putting it in the mailbox, so I think the “private express statute” applies just to “things that qualify as mail-type communications”, like flyers and letters, not things like the next quarter’s Sunday School materials or videotapes of Stargate episodes.
“Private express” also has the effect of giving the U.S. Postal Service an advantage over FedEx or UPS.
So do people who go up to Bloomfield and knock down mailboxes with a baseball bat commit a federal crime while doing so?
Just wondering, that’s all.
I believe so. We have quite a problem in our hometown in Texas with kids knocking down mailboxes. The victims apparently have trouble getting any action taken against the perpetrators, because the local cops say it’s a federal matter and the feds, of course, aren’t interested in such petty crimes.
That’s what my mother told me, anyway.