This story has that 'much ado about nothing' smell. This is the 'there's Commies in my attic' tag that consumed the brittle public and bozo officials during the Cold War. Those employers who are concerned methinks have already screwed up their workplaces.
Legal liability is also another bugaboo that suppose to scare everyone into palm sweating obedience.
Seems like if you gotta sue your friends for their email, then they're, uh, not really your friends. Wait did you hear the one about.