Deliverability & the inbox
Seed list
Also known as: seed test · inbox-placement testing
A panel of real test-email accounts across the major mailbox providers used to verify where a send actually lands — Primary inbox, Promotions, spam, or blocked. The only reliable way to measure inbox placement.
A seed list is the panel of 50-150 test email addresses held across Gmail, Outlook, Yahoo, Apple Mail, iCloud, AOL, and international providers (web.de, GMX, Orange, etc.). Each scheduled send includes the seed list as recipients, and a deliverability tool (Everest / Validity / GlockApps) monitors which folder each seed address received the message in. The aggregate result is your real-world inbox-placement rate. Seed lists are the only way to measure where your email actually goes — ESP "deliverability rate" just measures acceptance (didn't bounce), which tells you nothing about whether the message landed in Primary vs spam. For brands sending above 100K per send, seed testing is the cost of operating; below that volume many operators rely on Google Postmaster Tools plus manual checks.