Inbox placement
Whether delivered email lands in the inbox instead of spam.
Delivery only means the receiving server accepted the message. Inbox placement asks where the message landed after filtering. Seed-list tests and panel data can estimate placement, but no test perfectly represents every recipient inbox.
reading this as developers picking email infrastructure
The question here is which one a backend engineer would rather operate. That means SDK depth in the language already in use, whether a retry can safely be replayed, how much the event log tells you when a customer says the email never arrived, and whether the pricing curve stays sane as volume grows.
Applied to inbox placement, that means weighing developer experience, SDK breadth, idempotency keys, and operating track record ahead of the rest, against password resets, receipts, and magic links shipped from application code.