> The point is that essentially all governments have granted themselves that power, one way or another. They have the right to access any postal communications in transit.

Even if they claim that "right", they don't in fact read or copy everything, and doing so is radically different from selectively reading or copying certain things.

I also doubt that "essentially all" governments claim such a power at all.

I know that neither the US nor Canada does.

From either the US or Canada, the UK has always looked way, way too willing to give blanket authority to various government functionaries, at least on paper (and, I guess, trust in their restraint and adherence to tradition). Nowadays it's like you're turning into a total police state (and that adherence to tradition seems to have been badly eroded). Australia might go for it; they're pretty authoritarian there.

Most of the EU probably wouldn't allow it (and in fact the ECJ nixed an EU directive to do less on the Internet). I don't think anybody in northern Europe would go for it. France has floated some pretty spy-ey proposals, but I don't recall them suggesting copying everybody's mail, and would expect riots (maybe they'd do it, but they'd riot first). Maybe the EU as whole would allow it for mail after being softened up for a while with this electronic communication stuff, but not now.

I will admit that most of Asia and Africa seem like lost causes, with either weak protections or weak institutions. I wouldn't be surprised if many governments there would claim that power. I don't know about "essentially all". I don't know about South America; they seem pretty diverse.

> Even, I would hazard a guess, under a practical day to day USPTO given the rather broad readings of the Postal Clause in the past.

The US Patent and Trademark Office? I think you mean the US Postal Service. And you may be confusing the "Postal Clause" with the "Commerce Clause". At least I don't know of any particulary broad reading of the mandate to operate the mails. And "operate" is pretty different from "read".

Anyway, governmental entities in the US emphatically do not have and cannot claim any power to read mail en masse. Nor can it be granted to them by legislation.

"Amendment IV: The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized."

That "reasonable" bit has consistently been interpreted to mean that if you have a reasonable expectation of privacy in the ordinary course of events, then that expectation can't be violated by the government without a particularized warrant. The interpretation of the Fourth Amendment expanded in the 20th century, and I don't really know the early history... but I don't think the federal government could have gotten away with reading the mail even in the 19th, and it probably would have literally destroyed the US if they'd tried in the 18th.

If it had always been the case that all, or a large fraction of, letters were read in transit, then they might have been able to get away with it, but it never was. Such a traditional expectation becomes a reasonable expectation, and therefore has legal force under US constitutional law. And amendments win over the main body of the Constitution (because they amend it).

There's tons of case law that would apply a particularized warrant requirement to mail. It's not even slightly ambiguous. Even the current SCOTUS wouldn't question it. I'd expect 9-0, but could be disappointed and see 7-2. It wouldn't even fly for email or other electronic messages.

If they wanted to read all mail, or randomly chosen mail, or a large fraction of mail, they'd need a constitutional amendment. That requires a two-thirds vote in each house of Congress, plus concurrence of three fourths of the state legislatures. Substantive constitutional amendments are essentially impossible in the modern political climate.

If the Forces of Evil were on top of things, and twisted some arms behind the scenes with respect to the technology was originally deployed, maybe they could establish the "right" expectations with respect to the next means of communication somebody invents. That's a big, big maybe. But there's no question of them getting to read paper mail en masse. Not as long as the moral authority of the Constitution stands in the US.