If you’re like most small businesses, your revenue is largely dependent on engagement with your marketing emails. The lower your inbox rate, the harder of a hit you take on your marketing ROI. The problem is, most of us are unaware of what is actually happening to our emails after we click ‘send.’

About 61.25% of marketing emails never make it to the inbox.

Let that sink in for a moment: Only 40ish percent of your leads may actually be receiving your marketing messages. Talk about squandered ROI.

This leads one to wonder where your emails are actually going.

Oh Emails, Where Art Thou?

In fact, unless there’s something really, really wrong with it, Google will not reject an email. It’ll go to spam or get discarded but, on the mailer’s end, it will appear to have gone through.

Just because a receiving server pings back a successful transmission doesn’t mean it crossed the finish line. Beyond the delivery threshold, your emails still have spam filters to contend with.

You — the mailer — are completely oblivious to the potential loss you’re incurring. That is, unless you seed test.


What’s a Seed Test?

What Google (and all other ISPs) don’t tell you, a seed test will.

A seed test involves sending a tracked email to a collective of 799 to 1,000 monitored email addresses to gauge deliverability to a weighted sampling of mainstream ISPs and the internet at large. These seed list addresses — generated by your seed test service — exist at Gmail, Hotmail, Yahoo, AOL, etc. for the sole purpose of monitoring the path of your emails across the board. The question is: Are you hitting the inbox with these ISPs or are you not?

By running a seed test, you’ll learn the following:

  • Which specific ISPs are delivering your email to the inbox
  • How your list quality affects the delivery of your email
  • Whether the content of your email affects the delivery of your email
  • How fast your email is being delivered

Rather than just gleaning your marketing success from your open rates, you’re able to track the rate at which your emails are getting delivered in the first place — thereby putting the horse before the cart as intended.

When Should I Seed Test?

You can learn a lot about your list, your content and your mailing practices from seed tests. Rule of thumb: If you’re making any changes in your content or notice any sporadic fluctuation in your delivery, a seed test will do you well.


A dip in your opens could indicate that you’ve fallen out of grace with a particular provider. At this point, it’s good to verify which provider(s) aren’t treating you well. Then do some research as to what you can do to placate the ISP in question.


Maybe you’re adding an email template for the first time or making significant changes to your existing template. Even a less profound layout facelift can spell big changes in delivery. To preemptively dodge a headache, do yourself a favor and gauge your new delivery rate by seed testing.


As your business evolves, so does your voice. You may target a new segment of contacts to whom you communicate differently than your original audience. As with a change in your template, alterations to your brand voice can more or less impact your delivery. Test the delivery waters with a seed test before diving in.  


As innocuous as it sounds, even the hours at which you mail have bearing on your delivery — particularly if you’re changing hours to accommodate a new time zone. Not to worry; finding your sweet spot through the powers of deduction is another reason seed testing plays such a pivotal role in bulk email marketing.


Your list definitely has a pronounced effect on deliverability, and testing your list as it stands is a simple way to gauge how good or bad your list acquisition or list maintenance practices are.

To do this, send an email to only your seed list. Then later that day or the next day, send the same content to both your contact list (your planned blast) and seed list. If your first test (seed list only) performs better than the second test (seed list plus broadcast list), that’s a clear indication of reputation issues with your list. In other words, your list is bad. Conversely, if the latter test is the winner, your list reputation is helping deliverability, and there may be an issue with your content.


It’s wise to run monitoring tests any time you bulk mail your list. Let’s say you’re announcing an annual sale or promoting a new product. By mailing your list and your seed list simultaneously (to ensure that your list reputation is accounted for in your seed test), you’re able to see exactly where your emails landed, if there are issues with a specific provider, or any other issues. This practice is much more reliable than intently watching your open rate and praying it doesn’t tank.

Open rate is not the end all, be all of delivery. Don’t presume a steady open rate is an “all clear” sign. This week’s broadcast may have delivered poorly at Yahoo yet splendidly at Gmail. A week later your email delivers poorly at Yahoo yet delivers issue-free at Hotmail. If you didn’t seed test, you could be incurring heavy losses one way or the other and never know it.

These tests are bound to uncover gaping holes in your email marketing.

My Seed Test Results are Sub-par. Now What?

Check out the knowledge bases of each ISP; you’ll find best practices and guidance targeted to bulk senders on what the ISPs want to see from you as well as how to get to the inbox. Chances are there’s something you’ve overlooked or were previously unaware of.

If you’re an ONTRAPORT user, we recommend reviewing our delivery documentation and making sure you’re following those best practices. If you find yourself stuck, reach out to our delivery team, and we’ll be happy to work with you.

Start Using a Seed Testing Service

Using a seed testing service like 250OK, Return Path, or IBM Email Optimization  will help stop email deliverability woes by offering insight into deliverability, inbox rate, and reputation with the biggest ISPs.


Seed list optimization is one of the most beneficial tools a seed testing service can offer. Essentially, you can take your mailing list, put it into the software, and it will spit out a seed list that’s tailored to the distribution of your list.

Let’s say your list consists of 30% Gmail, 16% Hotmail, 10% Yahoo, and 2% Cox.net addresses. It will exclude or include the ISPs that have a presence in your list and weight the stats according to the distribution of ISPs on your list. Through these weights, you can get an accurate gauge of how your mail is being delivered to YOUR list, not all ISPs that exist.

If you were to conduct a seed test on an unweighted list, your overall unweighted inbox rate might read 70%. That statistic is not indicative of your true list. For example, the seed list could very well be bogged down by ISPs that don’t appear on your list.

Our Top 3 Seed Testing Tips

Once you’ve procured your preferred seed testing service, you’ll do well to use these tips to ensure (near) pristine delivery.


Bulk mail regulations constantly change, as do spam filters. In turn, your email inbox rates can fluctuate without you even knowing it.

Don’t just sign up for a seed testing service, run a couple of tests, and then drop it.  If you’re taking the critical step to sign up, actively monitor your reputation going forward. Though you may not run into any issues with your first few mailings, there could be a problem with the next one.


Email lists are by no means static. New providers sprout up often, and it’s not uncommon for existing providers to merge.

Given the ever-changing ISP landscape, the makeup of your list is going to evolve over time. For that reason, we recommend updating your seed list once a month.


When you first get access to your new seed testing service, play with it a little bit.

Try your content. Look at inbox rates for emails that have garnered good open rates in the past. Seed test those against emails that have had negative open rates. If this is your first time seed testing, by all means include your seed list on your next broadcast to your whole list. The resulting numbers are really going to tell you how you’re being delivered.

If you’re limiting your testing to content — and excluding your list — you won’t have a firm grasp on which is delivering well and which is not. Sure, it’ll give you a general idea of how your content will be delivered, but your list reputation is equally important.

About Martin Cogburn

Martin Cogburn, ONTRAPORT's Senior Content Strategist, cherishes and strives to master the art of great storytelling. Originally from Frankfurt, the German native attended UCSB after growing up in the Santa Barbara area. Martin wears multiple hats in his role at ONTRAPORT: story producer, blog author, scriptwriter, and content curator -- all of which get his creative juices flowing. On top of that, he's an avid film enthusiast. Name any movie and there's a pretty good chance Martin can tell you all about it.