Seeding a Mailing

Seed Testing and Inbox Placement

Before your email reaches a single subscriber, seed testing shows you exactly where it will land — inbox, spam, or blocked — across the ISPs that matter most to your audience. Use it to catch deliverability issues early, validate your sending infrastructure, and send with confidence.

What Your Results Show You

After running a seed test you'll see inbox placement broken down by ISP, showing the percentage of messages delivered to the inbox, routed to spam, or missing entirely. Results are split across two tabs — Consumer Providers and B2B Providers — so you can see exactly where your exposure is.

Your overall delivery percentage appears at the top, with a full breakdown by ISP as you scroll. Results begin appearing as they come in — the report can take several minutes to complete, so if you're seeing a large number of spam or missing results, click Refresh Results before drawing any conclusions.

Choosing Your Test Type

PostUp offers two ways to run a seed test depending on where you are in your workflow:

Integrated seed test — runs automatically when your mailing deploys. Set it up during mailing creation and the results will be waiting for you after your send. Note: integrated seed tests require a minimum list size of 10,000 and are not available for triggered mailing templates.

Standalone seed test — run this before you send to get results ahead of deployment. Useful when you want to check deliverability before committing to a send.

Running an Integrated Seed Test

1. Create or edit a mailing and navigate to the Seeding tab
2. Select the integrated seed test options at the top of the page
3. Choose your seed type:
   • Automated seeds — a preset seed list provided through Glock Apps, a third-party deliverability testing service
   • Custom seeds — add any email addresses you want to receive a copy of the mailing at deployment. For recurring and drip mailings, custom seeds are the only available option
4. If adding custom seeds, enter addresses separated by commas or one per line

Running a Standalone Seed Test

1. Scroll to the bottom of the Seeding tab to find the standalone seed test section
2. Select the recipient and list for the test if applicable
3. Click Run Seed Test to request your report — the button will grey out until you've viewed the results

Once you've reviewed your results the button becomes available again. Note that requesting a new report will replace the current results for that mailing — previous results remain accessible through the Reports tab.

Tips for Getting the Most From Seed Testing

Run it before high-volume sends. Catching a deliverability issue before a large campaign is significantly less costly than discovering it after.

Use standalone tests when trying something new. New content strategy, new segment, new sending domain — test before you commit.

Don't judge results too early. Give the report a few minutes to fully populate before making decisions based on what you see.

Check both tabs. Consumer and B2B providers can behave differently — a clean consumer result doesn't always mean your B2B delivery is healthy.