Under US law, it’s illegal to read another person’s mail with the intention of obstructing the correspondence or prying into their business or secrets (18 U.S. Code § 1702 – Obstruction of correspondence).
In most circumstances, it’s also illegal to intercept, disclose, and use phone conversations without the consent of at least one party (18 U.S. Code § 2511 – Interception and disclosure of wire, oral, or electronic communications prohibited).
