The last estate I liquidated, I created my own UPS shipping labels from the widows home. Bought a bunch of those 55x14x4 inch boxes on Amazon and packing material (bubble and brown paper).
I am not a licensed FFL but required a copy of the FFL that I was shipping to and then verified it here: https://fflezcheck.atf.gov/fflezcheck/

She shipped (via UPS, with assistance from me) long guns from OR to PA and places in between. The average cost of shipping was around $50 and buyer paid additional shipping once a price was determined.
A few of the long guns I included a UPS pick up at her front porch for $10 additional, charged to the buyer (included in price)

Sorry, that didn't answer the USPS question. Just giving you my experience.

^ Yes, but the registered/certified mail thing is not a requirement.

Here’s the USPS info:
https://www.atf.gov/firearms/qa/may-non ... al-service

A C&R license would work then, to ship handguns via USPS? The link above says 'licensee'. So a CL3 license is cheaper than shipping private carrier.

My understanding is that a C&R license is not sufficient, but I don't have any data to back that up. Maybe it's just a case of people being cautious, I don't know.

I had the postal worker call the Annex Manager, she told me they can't ship firearms, I told them they were wrong, and get me the postmaster, he was short and rude, categorically said "no firearms", "What happened if it gets lost or stolen?" So that's that. If you live in Bellevue with the same postmaster, you can forget about shipping as Individual.

If they're breaking the law contact SAF, sounds like a slam dunk lawsuit.

Keep taking it up the chain. Don’t let them get away with it.

print out their rules and stuff it under his smug fracking nose.

Have you tried using something besides logic? As in their own regulations?

From Publication 52:

432 Mailability
432.1 General
Mailers must comply with the Gun Control Act of 1968, all of the provisions of postal law in 18 U.S.C. 1715, and all other all federal and state regulations and local ordinances affecting the movement of firearms. The following also applies:

The Postal Service may require the mailer to open parcels containing firearms or air guns or give written certification that the weapon is unloaded and not concealable.
Short-barreled rifles or shotguns that can be concealed on the person are nonmailable.
No markings of any kind that indicate the nature of the contents may be placed on the outside wrapper or container of any mailpiece containing firearms.
Mailable matter must be properly and securely packaged within the general packaging requirements in DMM 601.1-7.
Except for shipments between licensed dealers, manufacturers, or importers, all regulated firearms must be mailed using a USPS product or Extra Service that provides tracking and signature capture at delivery.

https://pe.usps.com/text/pub52/pub52c4_009.htm

Apologies if this is a repeat...