The paper mill and the paper demand of the headquarter is part of a grander scheme, but I did not yet succeed in scripting the "grander scheme". So, for the moment they are, as you mentioned, a little of a waste. But who knows what the future brings for these two... ;)

Isn't it possible to condition the generation of mail on paper supply?
The goal is to make this industry profitable and add logic

I have tried to develop something like that. Paper brings organisation and efficiency. But I did not (yet) succeed in programming events upon the reception of paper by the HQ. It's mainly a problem of my lack of knowledge in programming with lua. But your idea is a good one.