That’s not what I’m talking about.

Responding to a company is responding to a request they made for your time.

That said, most contractors I’ve worked with would not bill for a short email saying they’re unable or unwilling to do some work as a professional courtesy. The contractors who literally bill and round up for every email are usually going out of their way to maximize billing, which is eventually accounted for in the rates we’re willing to pay for them. We learn quickly that certain contractors will bill and round up for everything, so the most we’re willing to entertain as an hourly rate for them is lower as we know they’re going to send arbitrarily higher amounts of hours over.