

If they send 2 emails per subdomain per year, that could easily be 10s of millions which would make the cost per email measured in thousandths of a cent. And I could see the number of subdomains being larger by a factor of 10, maybe more.
Another angle: someone with IT experience needs to manage the system that seems emails, and other engineers need to integrate other systems with the email reminder system. The time spent on engineering could easily add up to thousands per year, if not tens of thousands.
I’m guessing their figure is based on both running costs and engineering costs.
Not entirely true… If you write libraries for other developers you can use them as beta testers. Your customers have a production environment, but you don’t. At least, that’s what one of our vendors seems to think…