Iuliia Nesterenko

Technical Writer

What Marketers Must Know About Technical Email Testing [Webinar Recording & Takeaways]

People open emails on different devices and in different clients and the rendering variations can affect their display. Emails that look good on the desktop may be distorted on the tablet or smartphone. You can’t predict what device a person will be using to open your email but you can do preventive activities to ensure proper display on whatever device. Email testing is one of them.

Although many marketers see email testing as a challenge, it doesn’t have to be complicated as long as you know what to do and what tools to use.

To help, we asked Diana Lepilkina, a marketing specialist from Mailtrap, to speak about practical aspects of email testing and how to do it in the most effective way.

Listen to Diana sharing professional insights into email testing, performance testing, common email testing mistakes and more.

For those who are looking for the highlights, here is a short summary of lessons learned.

Key Takeaways

#1. Email Deliverability Issues

Email deliverability is more complex than it seems at the first glance. Not all marketers take it seriously, believing that email creation is the final step before hitting the Send button.

However, Hubspot suggests that on average only 25% of all sent marketing emails are opened, depending on the industry. A spam testing tool GlockApps suggests that on average 51% of emails never land in the Inbox: 26% of them go to Spam and 25% fail to get delivered at all.

Why it happens:

  • No single spam identification criteria. Email clients don’t reveal their spam filter algorithms so that spammers can't adjust to them and get access to your Inbox.
  • No single HTML rendering standards. Email templates with visual elements display differently across email clients.

Why it’s important to test emails:

  • Make sure your emails look as intended;
  • Guarantee email deliverability;
  • Avoid spam filters;
  • Protect your sender reputation;
  • Deliver satisfying user experience.

#2. Email Testing Approaches

Marketers generally divide email testing into two big groups:

Split testing or A/B testing: experiments with email content and subjects to improve the open rate and click rate.

Tech testing: tests of email infrastructure elements and error debugging. Typically such tests aim to solve one of the problems:

  • Incorrect email infrastructure (unable to send emails);
  • Poor deliverability (emails go to Spam);
  • HTML/CSS not supported (emails display incorrectly);
  • Broken links (expired links to limited offers).

Built-In Subject A/B Testing!

In eSputnik, you can A/B test your email subject lines straight within the system. You can add unlimited subjects to one email or create several emails with different subjects and send them to different contact segments.

A/B test report

#3. Email Testing Mistakes Marketers Make

  • Careless selection of an ESP (email service provider).
  • Ignoring tech email aspects (authentication, spam checks).
  • Focus on content check only;
  • No testing strategy or irregular testing.

#4. Full-Cycle Email Testing

Pre-sending:

  • Sending infrastructure;
  • Email template (copy, links, headers, HTML/CSS);
  • Email deliverability (spam, blacklists, email list hygiene);
  • Additional checking (campaign-specific).

Performance checking:

  • Opens rate, click rate, bounces, unsubscribes, spam complaints;
  • Split testing.

Although this may look like a lot of work, modern marketing software with extensive functionality makes it possible for one marketer to do the job. If you choose a professional email service provider and regularly validate your emails though a good testing tool, your campaigns will show the highest deliverability rate.

Last post

#5. Email Testing Tools for Marketers

Infrastructure testing tools

Email template display testing tools

HTML testing tools

Email copy checking tools

Subject line and preheader testing tools

Email deliverability testing tools


When you invest a lot of effort in your email marketing campaigns, you want to be sure it’s paid off. No marketer or designer wants to spend time crafting campaigns that will eventually end up in Spam or won’t be delivered at all.

To avoid such issues, make email testing part of your marketing strategy. Choose the right tools, from an ESP to email tester, define the metrics you want to test and scalable results you want to get. Most importantly, don’t do the testing for the sake of testing. If the same element (for example, template layout or spam words in the subject line) keeps on failing the test, consider revising the related tactics.

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Iuliia Nesterenko

Technical Writer

A technical (but still very creative) writer at eSputnik with a strong focus on design, current digital marketing trends, and new solutions for email automation.

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