... I have a user that thinks they need to check their email every > 30 seconds or so and I would like to restrict to every 15 mins or so. I > have told them they are doing this but the insist their business relies > heavy on email.
I guess they have a permanent connection? Maybe you could sell them a server for their office set to receive email directly via SMTP?
Out of curiosity, how much extra load are they placing on the server and is it really causing a problem? Do they check 24 hours a day or only when they are at the office?