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 early-stage startups
At an early stage the deciding factors are what the free tier actually covers, what the first paid invoice looks like, and how much of a founding engineer's week the setup costs. Feature depth that only matters at a million sends a month is noise until it is not.
Applied to inbox placement, that means weighing free tier, best published rate per 1,000, entry price, and developer experience ahead of the rest, against a waitlist, a launch announcement, onboarding email, and the first transactional sends.