A suggestion...
Since the USPS at some point turns mail over to others postal services to handle, inspect, and deliver, perhaps either UPS, DHS, or FedEx would give more continuity of responsibility.
I have not researched this, but thinking out loud.
I have shipped to Europe using Registered Mail, and I have been "assured" that such a package has hand-to-hand accountability (in this case it went to Italy).
If UPS, DHS, or FedEx ships a package, I am sure they still have to move packages through the foreign country's customs inspection. And if there are duties to be paid, then from what I have heard about packages not being delivered the packages will languish in customs until the local addressee actually pays those fees.
This in turn suggests that when sending packages overseas the sender should make two photocopies of the outgoing package with all labels and stamps showing, and send a copy to the recipient via the mail or email so that person will have hard facts to work with at their end.
Others will know more about this than I do, but maybe the above will help to bring them forward.
Larry
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Larry W. Williams
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