It might be because the service sends both spam emails and legitimate emails. Many (maybe even most) sites do this. If this person is getting a thousand emails

It might be because the service sends both spam emails and legitimate emails. Many (maybe even most) sites do this. If this person is getting a thousand emails over the course of a few years, how on Earth are all of those legitimate, especially when they've only replied to a handful of them, implying the majority of emails can oe safely ignored.