

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.
Nothing to worry about unless you’ve signed a contract with someone. Normally when you sign with a record label you’re selling them the rights to your music, so they could sue you if you try to give it away or sell it without them being involved. Record labels are known to be pretty predatory…