[drsim]

I have a B2B app too, and get email from people who are downright rude. I wouldn't bundle the OP in with this bunch: he just seemed frustrated.

But as the service provider it's your responsibility to maintain a professional tone. When I get what, at best, are difficult customers, my approach is to be tersely polite. Then half tend to back down and be apologetic, the other half I never hear from again.