Buncha Microsoft bootlickers in here.
Why does it matter that the service someone is paying for is an api or something else versus email? The email service failed. First and foremost Microsoft’s service failed. It doesn’t matter HOW it should be engineered.
We all know that services can fail, and consequently will fail at some moment. It is therefore primarily the responsibility of the designers of this system.
They should have closed the pool.
Email as the sole notification source for a safety critical situation is criminal, in the literal “the responsible engineer or coder masquerading as an engineer should be in jail” sense of the term.