In the UPS info...
"Any item that meets the definition of a firearm (including firearm mufflers or silencers) or a “frame” or “receiver” under federal law (including any partially complete, disassembled, or nonfunctional frame or receiver as defined by 27 CFR § 478.12) must be identified and bear a serial number in satisfaction of the requirements for identifying such items under federal law, including 27 CFR § 478.92 and/or 27 CFR § 479.102, regardless of whether any such items are otherwise exempt from or not subject to identification requirements under applicable law. This prohibition applies even before the effective date of 27 CFR § 478.12."
I think this says that all firearms must have a serial number regardless of whether it is required by law. A lot of older .22 are not serial numbered.
Realistically:
Are they going to tear your package apart to make sure the gun you are shipping has a serial number on it?
It's not legal to drive 66 mph in a 65 mph zone. You could get a ticket for that. But nobody does.
What is the punishment for shipping a gun or gun part against UPS "policy"? A good tongue lashing from the clerk or supervisor? It's not even against the law. It's against their policy. UPS is a private company. They don't make laws. They are not a legislative body.
Holy sheet....