Seed List

What It Is

A seed list is a small set of test inboxes you send to consistently so you can measure deliverability signals:

• inbox vs promotions vs spam
• provider-specific differences (Google vs Microsoft vs others)
• stability over time

It is not a replacement for real-market results. It is an early-warning system.

Why It Matters

Most teams notice deliverability issues too late because they watch lagging indicators:

• reply rate dropping
• booked meetings slowing down
• “it feels like we are landing in spam”

A seed list gives you leading indicators so you can fix issues before they damage your sending reputation.

Related: Inbox placement

What A Good Seed List Includes

Minimum viable seed list:

• 3-5 inboxes on Google Workspace
• 3-5 inboxes on Microsoft 365
• at least 1-2 consumer inboxes (Gmail, Outlook.com)

If you sell internationally, add geo diversity.

How To Use It

A simple weekly operating loop:

1. Send a consistent test email (same subject/body structure)
2. Record placement per inbox
3. Compare against the previous week
4. If placement worsens, reduce velocity and investigate

Investigation checklist:

• authentication issues (SPF/DKIM/DMARC)
• sudden volume spikes (lack of throttling)
• list quality issues causing bounces

Useful adjacent concepts:

• SPF
• DKIM
• DMARC
• Email throttling
• Bounce rate

Common Mistakes

• treating seed placement as “the truth” (it is directional)
• changing the email template every day (you lose comparability)
• ignoring velocity (seed lists often degrade when you spike volume)

For the full system approach, see: Outbound infrastructure and Cold email deliverability.