In general, the legal principle is that privacy rights apply to living people, it is considered that dead people are incapable of being harmed by invasion of privacy or defamation - or, in general, pretty much everything else; they have literally stopped caring about worldly trivialities like that no matter what version of afterlife you prefer.

Even for inheritance, while we in general mostly respect the wishes of the deceased, there's a principle to limit what future conditions they may impose on handling the property, to ensure that "the dead hand" does not govern over the living because the wishes of the living matter more than the wishes of the dead.

So the whole notion of post-mortem privacy is centered at protecting the interests of living people e.g. the reputation of surviving relatives. If some horrible act is performed against a dead person, the relatives or the community may claim that their rights have been violated, but the corpse itself has no rights. If you are dead, your most private correspondence can be viewed by others and distributed to the public as long as the rights of any living people (e.g. the other party in the correspondence or your relatives) are not violated.

If the privacy laws of today manage to protect your library lending habits 90 years after your death, then these will truly be dark days for future historians.