There is a long history of tampering with the mail. It wasn't merely the preserve of the Stasi et al. It's one of the reasons most countries sought to retain

There is a long history of tampering with the mail. It wasn't merely the preserve of the Stasi et al. It's one of the reasons most countries sought to retain government monopoly until comparatively recently. https://en.wikipedia.org/wiki/Postal_censorship https://en.wikipedia.org/wiki/Postal_censorship