You don't buy the cheapest parachute.
Transmit is live. A transactional email API is the thing that has to work when you are not in the room.
Nobody noticed. That's the job.
Notes on mail that has to arrive, from the people on the hook for it.
The party line.
Most transactional email goes out on a shared line. It's fine until the morning it matters.
The receipt.
The API says accepted. It does not say delivered. The difference is the whole product.
Your reputation. No roommates.
One verified domain per account. It reads like a restriction. It's the vetting.