Email Space Monkeys: Use Seed Data to Test Your Campaign before Hitting "Send"

If you’re anything like me, you might think of an email campaign as a space ship… Okay, maybe that’s just me.

As we all know, just like rockets and other spacecraft, some email campaigns might fly through the metaphorical heavens while others may never get off the ground. As legendary aerospace engineer Burt Rutan, the brains behind Voyager, once said, “Testing leads to failure, and failure leads to understanding.”

What if you could apply that same idea to your next big email campaign? How might you better “understand” where the problems might lie? Will it soar or flop? Find out before the countdown to hitting “send” by testing with seed data, the space monkey of campaign deployment.

Let’s back up a bit and start with a few basics: Return Path’s Inbox Monitor is a powerful measuring tool designed to confirm that your campaign emails arrive in the inbox based on several data factors, including Return Path seed data. So what are seeds? Our seed list is comprised of email addresses maintained by Return Path to which senders deploy mail in order to approximate deliverability rates with internet service providers (ISPs). This includes even paid-service ISPs and internationally exclusive accounts.

So where might the testing part come in? While we always recommend including the full list of seeds with any send file you’d like to track, it is also possible to send a campaign to only the seed list, in order to identify any potential failures and understand how your campaigns can get off the ground.

Ready for takeoff?
Be the first to find out if there are any reasons why your campaign might not get off the ground—before your recipients do. Here we will weigh in the benefits and even discover a few black holes with testing. Let’s explore a few of the benefits to testing your campaigns:

  • Find out how your campaign will perform against the seed accounts. Each seed is designed to give you an accurate depiction of how your message will perform at individual mailbox providers. Depending on the regions you intend to reach, you can even identify how your message might perform around the world. Seed data will provide a whole world of information, but starts with the three basic metrics: what percentage of mail goes to the inbox, what percentage reports as spam, and what percentage goes missing.(Mission control reminder: when you send an email campaign you plan to monitor, make sure to include the entire seed list. For the most accurate representation, we recommend distributing the seed addresses throughout your list alphabetically.)
  • Seeded campaigns will test against Return Path’s Inbox Optimizer, which runs a series of more than 25 diagnostics designed to notify the sender of any (as Burt put it) failures. The good news is, by testing to the seeds, you’ll know of any problems before anyone on your actual send file. These diagnostics include everything from authentication and list-unsubscribe to image-to-text ratios and size limits. Here is a snapshot of that diagnostic report. (Notice the problem factors highlighted in red, which includes a “how-to-fix” link as well.)


  • Some mailbox providers will heavily consider content when deciding what will get through the gateway. If you have a creative idea on content, and want to be sure of a new image, link, or anything out of the norm, test it! You can send a test file to the seeds and create a compelling A/B test to find out what might working and what might be holding your delivery back.
  • In many cases mailbox providers will throttle delivery if you are warming a newly designated sending IP address or even sharing an IP address. Know for sure what your delivery might look like with a seeded test campaign. The deliverability metrics that the seed data provides will give you an understanding of what is getting to the inbox and what isn’t. (Houston, we have a problem! Although rare, there is one black hole of seed list utilization: never use the seed list alone to warm an IP.)
  • We all know the domain composition of every send file is different. One of the many fancy features Return Path offers is mailbox provider weighting, which is designed to show the best representation of deliverability based on how a send file breaks down by mailbox provider. Our default seed list is designed to show a sample size of mailbox provider relevance for email overall. However, on the mailbox provider weighting page in our UI, you can adjust the delivery statistics to reflect mailbox providers that have higher representation on your mailing lists. Applying this weighting strategy works for test campaigns too! So, if you have a high population of Gmail recipients for example, apply the proper weighting to reflect seed data even more accurately.

Testing your campaign prior to hitting “send” is certainly not required to have a successful campaign. However, much like the pioneering the space program, testing, testing, and testing again will pave the way to the stars.

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