epistlepredation

The act of preying on another's private correspondence;
"espitlepredator" - one who does this (also known as an espistlepeeper); also, "espistlepredatory"

Usuage:

"People who peep into other people's letters are peeping into other people's lives. It is a particularly pernicious invasion of personal privacy sometimes known as "espistlepredation".

Epistlepredators seldom go to jail, but they sometimes receive nasty letters addressed to other people designed to discourage their epistlepredatory practices."