Inbox placement
The percentage of delivered emails that land in the recipient's primary inbox rather than spam or Promotions.
Inbox placement is the percentage of emails that land in the recipient's primary inbox, as distinct from spam folder, Promotions tab (on Gmail), Other folder (on Outlook), or quarantine. A 98% delivery rate sounds great until you find out 40% went to Promotions and your engagement metrics tanked.
Inbox placement is monitored via seed lists (test addresses across major providers) or via panel-based services like Validity or 250ok. The gold standard for measurement is panel-based — actual inbox placement from real recipients across providers. Seed lists are cheaper but less representative.
Improving inbox placement is the deliverability discipline in shorthand: authentication right, engagement strong, list clean, content reasonable. There's no single lever; it's the integrated outcome of doing all of the above well.