Outbound Glossary
Seed list
Your own test mailboxes across the main providers, used to see where a campaign lands before the prospects do.
A seed list is a set of accounts you control at Gmail, Microsoft 365 and whatever else your market uses. You include them in a send and then look at where the message ended up in each one.
The honest caveat is that seeds behave nothing like prospects: they do not reply, do not file mail and have no history with you, so they tend to show a rosier picture than reality. Use them to catch a broken setup, not to prove a campaign works.