Seed List Testing: How to Make Sure Your Emails Perform Perfectly

Mike Arsenault
July 21, 2021
minute read

Before you send out a new email campaign, you always need to test it and make sure that it looks right in the environment where your subscribers will see it.

There are a huge number of devices, email programs, email providers, and browsers. So, your emails must display correctly across a massive number of screen type and user interface combinations. Also, your emails need to traverse a variety of spam filtering infrastructures.

So, there are many variables to account for and testing your emails in all these environments can be tricky.

That’s what seed list testing does. It checks two things that have a significant impact on marketing email performance:

  1. Check to find out if your email is passing email authentication and spam checks, and reaching subscriber inboxes.
  2. Check to make sure your emails display correctly in the most relevant browsers and email interfaces, so people actually read them and take action.

Here’s everything you need to know to create your seed list and start seed list testing. We’ll start with the ground-level basics.

What is a Seed List?

A seed list is a list of email addresses that you send emails to before you send them out to your subscribers. Your seed list should have emails from various email service providers and ISPs. This way, you can make sure your emails pass all the different spam filters and display correctly across multiple user interfaces.

In short, your seed list will show you how your email looks in different email clients (i.e., Gmail app, Yahoo!, Hotmail), in different browsers, and on different devices.

Traditionally, companies used employee email addresses for their seed lists. Some companies create test emails specifically for seed list testing. Then, some businesses outsource the process entirely and let experts who specialize in email testing manage the lists and run the tests.

Outsourcing the process is often the most cost-efficient option when you account for all the time and effort it takes to create and manage the seed lists.

There are two types of seed lists: weighted and unweighted.

A weighted seed list is designed to be a cross-section of your entire email list. A weighted seed list enables you to test your emails in the environments where they’ll be seen in the wild.

An unweighted seed list is not built to be a cross-section of your email list. Usually, an unweighted seed list is built with specific factors for troubleshooting.

Your email seed lists don’t need to be huge. Just large enough to make sure your emails deliver and display correctly on the devices, browsers, and email clients that the majority of your subscribers use.

It’s best if you have both weighted and unweighted seed lists. These lists enable you to identify issues in a real-world environment, then isolate those issues and correct them.

Why Do I Need to Create Seed Lists?

If you’re familiar with email deliverability, you know that deliverability issues can damage your sender reputation. Testing your emails on your seed list helps you identify any authentication or spam filter issues that would hurt your sender reputation and cause even more deliverability headaches if you sent emails to your entire list with those problems.

Additionally, your seed lists save you from sending incorrectly formatted or unpolished emails to your subscribers. This spares you a lot of embarrassment. And, it ensures that people can read your emails and get value from them, so they don’t unsubscribe.

In short, seed list testing helps you make sure that your emails are technically sound, and that they deliver a good customer experience.

Email Deliverability: The Ultimate Guide to Keep Your Emails Out of the Spam Folder
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How to Run a Seed List Test

This might seem obvious, but you need access to all the email inboxes that you use for seed list testing. And, make sure that each seed email account you use has a first name and last name in the contact information.

The first step is the easy part: send your email to your seed list.

Then, check the inboxes and evaluate your seed emails.

  1. Check to ensure that your emails were successfully delivered to the inbox.
  2. Make sure your subject line, preview text, and recipient name appear correctly.
  3. Open the emails and ensure that they display properly. Check for image and text alignment, and that you can see everything.
  4. Click all the links in your emails.
  5. Open your emails on multiple devices, browsers, email clients, and ISPs. This will help you identify display or function issues within the different interfaces that your subscribers use.

There are tools that help you automate this process. These tools provide software and analytics for assessing your emails. If you’d like to use a seed testing tool, these are two of the best:

  1. GlockApps.
  2. 250Ok.

Both services are excellent for testing deliverability and inbox placement. However, even if you use a spam testing service, it’s still wise to open your emails yourself to check the display and function.

The seed list test itself is a fairly quick and straightforward process. It’s the troubleshooting that usually takes more time. But, it’s worth it to know that you’re sending out high-quality emails, that land in subscriber inboxes.

Understand that seed list testing is designed solely to make sure that your emails get delivered, display correctly, work the way they should. Seed list testing does not measure user behavior or engagement.

However, seed list testing will help you discover if your email performance metrics are being impacted by issues with your emails, that are unrelated to subscriber behavior. For instance, if your click-through rates are unusually low, a seed list test will show you if there’s a display or function issue with your CTA button.

Seed list testing provides an unbiased environment to test what will happen when you send emails to subscribers who use various inbox providers, ISPs, browsers, and devices. This gives you the data you need to determine what’s actually causing email performance issues.

Without seed list testing, you could end up revising your email subject lines and content, when the real issue is related to email deliverability, display, or function.

So, run your seed list tests before you get deep into A/B testing subject lines, CTAs, layouts, and all the other aspects of email. Otherwise, you could end up chasing a red herring.

Overall, seed list testing enables you to perfect and polish every aspect of your emails—from deliverability to aesthetics—before you send anything to your subscribers. That way, you put your best foot forward in every email you send.

What To Do Now

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Mike Arsenault

Founder & CEO

For the last 10 years, Mike has worked with brands like Moosejaw, Hydroflask, Peak Design, Triumph, Hearst & Guthy Renker to provide the strategy & technology with which they use email to drive revenue growth. He's also the Founder of Rejoiner, a SaaS marketing platform built for ecommerce businesses.

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