# Seed testing

> Seed testing sends your email to a controlled panel of inboxes to estimate folder placement. What it can tell you, and the limits of testing on seeds.

Canonical: https://emailfast.dev/glossary/seed-testing

Seed testing is sending a copy of your email to a controlled panel of mailboxes, operated by you or a testing vendor, at each major provider, then recording where every copy lands: inbox, spam folder, or a tab like Promotions. It is the standard way to estimate folder placement, because ordinary delivery metrics cannot see folders.

## Why it matters

A 250 OK from Gmail means Gmail accepted the message, not that anyone will see it; spam-foldered mail counts as delivered. Seed tests are the only direct look at placement, and they catch concrete, fixable problems before a full send: broken [authentication](/glossary/email-authentication), a template that trips content filters, or a sending IP that landed on a blocklist overnight.

## In practice

A seed list spans the providers your audience actually uses. You send to it, collect the results, and read the pattern: inboxing everywhere except Outlook points at a Microsoft-specific reputation problem, while spam-foldering everywhere points at authentication or content. Then come the limits, and they are real. Seeds are not your audience. They have no engagement history with you, and modern filtering is heavily personalized, so Gmail may inbox your message for a subscriber who opens everything you send and junk the identical message for a stranger. Treat seed results as a smoke test and a direction, not a measurement of what your subscribers experience.

## How Email Fast handles it

Placement testing is integrated into Email Fast's pipeline and arms at launch with a seed-list provider, alongside a rendering matrix that shows how a message displays across mail clients. Until then, the same pre-send checks that seed tests catch mechanically, authentication and content problems, are enforced at domain verification and admission.