I treat everyone's email the same: I don't read it. I may see subject lines but I don't see the technical reason requiring you to read them.
What happens when you get a request from management to help them identify/bring to their attention people potentially 'abusing' the e-mail system, such as by e-mailing sensitive information out of the organization, or by identifying employee(s) sending e-mail that are obscene, abusive, harrassing, or contain inappropriate language?
That's an official request from management and is part of your job at that point even if it wasn't before. Inform HR of what you've been asked to do and if there's a conflict let them hash it out. Document everything and keep a personal copy of the documentation in a safe offline place. If you get fired for doing your job you either have enough documentation to take legal action (if you can afford it) or enough to clear your name if it becomes necessary.