Spam trap
An address used to detect poor list acquisition or hygiene.
Spam traps are addresses monitored by anti-abuse organizations or mailbox providers. They may be pristine addresses that were never opted in, or recycled addresses that used to belong to real people. Hitting traps is a strong signal of purchased, scraped, or stale lists.
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 spam trap, 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.