Yes, but that parallel example is not relevant here because modern online messaging is profoundly different in crucial ways. Governments can (and do) intercept and store nearly all electronic messages which permits instant searching and deep cross-referencing of all content and sender/receiver metadata for every message ever sent by anyone, anywhere, at any time. None of which is true for physical mail. If you don't find that terrifying, you don't fully understand what it means.

When they do intercept physical mail messages, if the sender has encoded the message, in most democracies, the government is not permitted to compel the sender to decode the message. And even if you come under suspicion today and they start intercepting your physical mail, they can't have an LLM read ALL the physical letters you've ever sent at the press of a key. With electronic communications they don't even need suspicion first. The LLMs are already actively searching everything hunting for anything the government labels sufficiently "suspicious." The "Five Eyes" intelligence agencies have been capturing all email, instant messages and phone call metadata for more than 15 years already.