Also called: seed test
An inbox placement test sends mail to a set of seed accounts across major providers and checks where it actually lands, primary inbox, promotions, or spam, before a domain or campaign goes live to real prospects.
The test itself is simple: send to a set of seed inboxes spread across the major providers, then check placement. Landing in the primary inbox is a pass. Landing in spam or promotions is a fail, and a fail means going back to fix the setup and testing again, not sending to real prospects anyway and hoping. That pass/fail framing is what makes it a gate rather than a metric to eyeball.
The test means the most once the pieces before it are actually in place. Authenticate the domain first, SPF, DKIM, DMARC, and confirm it passes with a real header check, not a glance that it looks configured. Warm the domain at a sane volume before the real batch, not the day of. Only then does the seed test against the drafted batch tell you anything about the content itself. Run it before authentication and warmup are solid, and a failed result could mean any of three different problems.
Tools like GlockApps automate this across providers, since checking every major mailbox manually doesn't scale. Corporate mail sitting behind a gateway like Proofpoint is the hardest case, there's no aggregate placement dashboard for it at all, so reply and open behavior from those specific domains ends up being the closest real signal available.
This isn't a check to clear once before a program launches. It's a gate rerun before every new sending domain and every new client goes live, since a domain that placed cleanly last quarter says nothing about one spun up yesterday. Teams that treat it as a one-time box to tick are usually the ones surprised when a new domain underperforms for reasons nobody can explain.
The test gets treated as optional once a team already has a working sending setup elsewhere. It isn't transferable between domains. Each new domain and mailbox starts with zero reputation regardless of how well an existing one performs, so skipping the seed test on the new one just delays finding out about a problem until real prospects are the ones who hit it.
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