Politically correct is intellectually abhorrent. One of our great gifts is the ability to laugh at ourselves and each other. One of the ways we're able to do this in modern times is via e-mail. If I'm compromising company well-being or my own contributions, fire me. If I'm harassing someone, they should tell me, and I won't.
Communication demands the exchange of ideas, and mutual respect.
Don't degrade the process by imposing blanket arbitrary standards. If you don't want any personal communications on company time, don't expect to have any personable people working for you.