Glossary
Seed list
Also called seed testing, inbox placement test.
Last reviewed 18 September 2026
What is a seed list?
A seed list is a set of addresses you control at several mailbox providers, mailed alongside a real send so that you can open each account yourself and see which folder the message landed in.
It exists because no provider reports inbox placement back to a sender, so the only way to observe the difference between delivery and deliverability is to be the recipient. A handful of accounts at the providers your readers actually use tells you more than any score a tool will sell you.
Treat the result as an indication rather than a measurement. Seed accounts have no reading history, no contacts and no engagement, and filtering is personalised, so a message that reaches a seed inbox can still be filtered for a reader who has never opened one of yours.
See also
- Deliverability
Deliverability is the share of the mail you send that reaches the inbox of the person you addressed it to, as distinct from delivery, which is only the share the receiving server accepted rather than bounced.
- Sender reputation
Sender reputation is what a mailbox provider has learned about the domain and the infrastructure your mail comes from, assembled from complaints, bounces, spam trap hits and how the people who receive your mail behave, and it is what decides the folder.
- Delivery rate
A delivery rate is the share of a send that the receiving mail server accepted instead of bouncing, and it says nothing at all about whether any of it reached an inbox.
Read next
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