[tsukikage]

...as disconnected from "email marketing services" as possible, please, because IME gmail is wise to those and files email associated with them directly in the trash regardless of all other concerns.

I suspect the reason SES is an exception is because it is very widely used for things like e-tickets, transaction confirmations and so on, and also goes to a nonzero amount of trouble to dissuade marketers rather than having them as the main customers.