How Email Testing Affects Deliverability

Sweat the Small Stuff: How Email Testing Affects Deliverability

Remember the time you opened an email from one of your favorite companies, and it looked like a garbled mess?

You can see some text, but it doesn’t look properly aligned. Images aren’t even loading, which leaves a bunch of empty, grey areas. Clearly, something is off about this email’s formatting.

All these issues and more prove why you should always test your email campaigns.

Email testing affects not only the look of your sends, but can also have a direct impact on your efforts to get emails into the inbox.

In the rest of this post, we’ll take a look at why email testing matters, how it affects email deliverability, and what you can do to start testing your email campaigns today.

What Is Email Testing and Why Does It Matter?

Email testing is where you evaluate the emails you want to send for inbox rendering, readability, and even things like link validation and your potential for being marked as spam. This process is similar to A/B testing or split testing for websites and UX design.

Essentially, email testing helps you preview what your email will look like across various email providers, browsers, and devicesso you discover any issues before you send and therefore deliver a unified, positive experience to your subscribers.

This process is important for email marketers to follow because not all email clients display your messages the same way. This is also the case for different browsers, and devices, which can physically show only as much as their screen sizes and backend coding will allow.

In fact,according to email testing and analytics company Litmus, every email you send has more than 15,000 possible renderings thanks to the factors mentioned above.

That being said, Litmus also found that testing your emails before you send them increases ROI. The company discovered marketers who tested their emails more frequently saw an ROI of 44-to-1, compared to an ROI of 38-to-1 from marketers who tested email rendering less frequently or not at all.

How Email Testing Impacts Deliverability

While better user experiences and improved ROIs are definitely benefits of email testing, why should you care about pre-send tests for deliverability? After all, as long as your emails reach the inbox, they were delivered, right?

Sure, technically they were. But email testing (or the lack of it) can have a direct impact on your overall sender reputation, performance, and therefore deliverability.

The reason is because the better experience a recipient has with your email content, the more likely they are to engage with it. The more likely they are to engage, the better your sender reputation becomes and the higher chance ISPs will deliver your future messages to the intended inboxes.

Think of it this way: if that garbled mess of an email you once saw had actually looked great, and every email from that company continued to display well in your inbox, you’d want to keep opening them, wouldn’t you?

It’s the same with the emails you send your own subscribers. The more consistent you can make these emails look, the more likely recipients will know exactly what to expect and will open each message you send.

How You Can Start Testing Emails Today

Now that you know why email testing matters and how it affects your deliverability, how can you conduct your own tests? And what should you be looking for when you get started?

Previewing your emails involves many different factors, but these are five of the most important ones you should pay attention to!

Images, GIFs, & Videos

Media content like images, GIFs, and videos are one of the biggest stumbling blocks for providing a consistent email experience to your recipients. Many times, these media types aren’t fully supported across all email providers.

Media can also be blocked or prohibited in some way or another by email clients, and individual users can adjust their personal settings to automatically block media from displaying in their inboxes. And by default, many corporations block images and media content across all company email addresses as a safety precaution.

This means that all the work you might put into selecting, editing, and embedding the right media for each of your emails will be a waste of time. Your images, GIFs, or videos will either not show up at all, or will appear to be broken. Either way, this is not a good look.

Fortunately, you can do some things on your end to mitigate the effect of media blocking and display issues:

  • Get into the habit of not expecting your media to load in inboxes, and stop sending emails laden with such content.
  • Provide ALT text for each image, GIF, or video so even if they don’t load, recipients still see something in their place.
  • Ask subscribers to whitelist your emails and/or add you to their safe senders list.
  • Make CTA buttons out of text and a colored background instead of using an image.

Layouts, Themes, & Designs

How often do you change the styling of the emails you send? This timing needs to be taken into consideration during email testing, too. For example, Litmus found that 40% of marketers redesign their email templates at least once a year, while 42% do so at least once every two years.

If you’re one of these email marketers who updates your design frequently, be aware you need to test its appearance every time you change it. This is especially important if you send out one-off emails with their own unique designs, such as for major announcements or seasonal offers.

Email Clients

With hundreds of email providers available to consumers, chances are very high your recipients are not all using the same provider. And, like it or not, email clients will also render your emails differently than another client will (like the media content described earlier).

Testing your emails across the top ten most popular email providers used by your subscribers is one way to ensure they all receive the same, if not similar, experience.

Devices & Screen Sizes

Similar to email clients, every type of device your recipients might use, whether those are laptops, mobile phones, tablets, or desktop computers, will often display your emails differently (think about the scale difference between a mobile phone and a desktop computer, for example). Even browsers and operating systems can show email messages in their own way.

Again, this is another reason why previewing your emails is so important! If you can find out which types of devices your recipients use to access your emails, the easier it will be for you to test your messages for those devices.

Coding Changes and HTML

Finally, no matter your best efforts to preview emails based on all the factors above, email clients, browsers, and operating systems for various devices can still change their coding and display rules at any point in time. For example, an email provider could change the way they used to display your email’s HTML so that an element no longer renders.

While you may be aware of some of these changes ahead of time, it’s always best to keep an eye on the market. Make sure you have an idea of what new devices are being released, what updates and changes are hitting browsers and operating systems, and what developments top email providers are making to their platforms.


In short, if you want to provide a consistent experience to all your recipients, you need to prioritize email testing. Otherwise, you may lose subscribers who don’t want to deal with your inconsistently formatted messages, which will affect your overall sender reputation and therefore your email deliverability.

Email testing may take extra time and effort, but the benefits are clear: a better user experience, increased ROI, and higher deliverability. It’s a win all around.