My host doesn't do support through their forum, either, but they're a lot more clear about the fact than Bluehost seems to be. I'd take the 'If you don't like it, go away" response that you got as just a flame from an idiot, moderator or not.

I don't offer a newsletter, but these kind of problems come up regularly in my host's forums, too. The only answer seems to be to use a separate program (dadamail, mailman, etc.). They allow you to split up your emails into groups which won't choke in your host's throttling scheme.