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Looking for an Email Renderer? Here’s What You Need to Know


As human beings, we all see the world differently, right? The way you interpret a story, a song, or a painting will be different from your friend’s interpretation. While email clients are far from human – they are a little bit like that too.

Gmail, Outlook, Apple Mail, AOL, and Yahoo Mail – they all interpret email campaigns in their own ways. When we say “interpret,” what we’re really talking about is email rendering.

Maybe you’ve only recently come to realize this, but how your marketing emails look in one person’s inbox could render quite differently for another subscriber. For instance, everything may display perfectly in Apple Mail, but things look messed up in desktop versions of Outlook.

We’ll explain what’s happening here and let you know what you can do about finding an email renderer that shows you what to fix before you hit send.

What is email rendering?

Here’s a basic explanation of how email clients render emails…

Whether you use a drag-and-drop editor or develop emails in-house, there is code behind the design of every campaign. Email clients like Gmail, Outlook, and Apple Mail have varying support for HTML and CSS as well as certain file formats and media. That’s one reason why there’s such a big difference between coding emails vs websites.

Email rendering occurs when a message containing HTML and CSS reaches its destination. Before an HTML email is opened and displayed, a rendering engine (which browsers use too) will process it. Rendering engines are pieces of software that essentially draw text and graphics on the screen, adding structure and style based on the code. Email code is like the instructions on how a campaign should look and function.

But if I gave you instructions on how to draw a cat, and then gave someone else the exact same instructions, we’d still end up with two very different looking cat drawings. That’s because we all have different minds.

Likewise, email clients use different rendering engines, and that’s why you get inconsistent results. Or at least, it’s one of the main reasons why.

Why is email client rendering a problem?

If we only had to worry about a handful of popular email clients, maybe rendering inconsistency wouldn’t be such a big deal. Unfortunately, it gets much more complicated than that.

There are thousands of possible ways an HTML email could render. That’s because there’s more than just the rendering engine at play here.

For starters, there are preprocessors that messages go through before reaching the rendering engine. These preprocessors try to remove code that could present security risks, but sometimes they remove things that cause rendering issues. Preprocessors for different email clients can even change the code before a message is delivered based on what they believe to be secure.

There are also different types of email clients, including web based, desktop, and mobile clients. Operating systems and screen size can have a major impact on the inbox experience. You’ll find, for example, that an email client may support some CSS when rendered on iOS, but not on Android. Or that what works for a web-based client fails in a desktop client.

To make matters even more complicated, certain email service providers (ESPs) may also alter or strip certain pieces of code from an email you’ve developed.

Finally, the preferences and settings of individual subscribers affect how an email is displayed as well. The way your email campaign renders may change drastically if a recipient is using dark mode settings. They may also adjust text size within their chosen email client, or they may have image downloading turned off.

For more on how complex it gets, check out the explanation from Chad S. White of Oracle Marketing Cloud.

Is there such a thing as an email renderer?

Can you find an email rendering service? If you’re looking for a piece of software called an email renderer, you won’t find one. However, there are ways to see how your emails are likely to render before you launch a campaign.

Back in 2020, we partnered with Holistic to find out more about how marketers address email mistakes. Our survey revealed an even split between those who send test emails to colleagues and those who use an email testing tool. A smaller percentage of senders have dedicated inboxes set up for email testing.

Pie chart of how marketers test email rendering

So, you can do it manually (aka the hard way), or you can automate the process and preview email campaigns with ease. Let’s take a look at both approaches.

The manual way to test how emails render

The manual process for testing how an HTML email renders involves sending a test email to colleagues in the organization and asking them to check it out.

That means you need to reach out to Cindy in HR and ask her to make sure your campaign looks okay on her iPhone 11 in Outlook. Then ping Carl in Accounting to have him do the same on his Pixel 6 in Gmail with dark mode settings turned on. And so on and so forth…

As you can see, this method is hardly reliable or comprehensive – even if you keep the testing within the marketing team. It’s also time-consuming, unorganized, and leaves a lot of room for human error. People who aren’t close to the campaign may not even know what to look for. Thankfully, there is a better way…

How does Email on Acid test email rendering?

We built Sinch Email on Acid to help you address email rendering inconsistencies in a more efficient and effective way. Technically, we aren’t an “email renderer,” meaning our platform doesn’t render the emails for you), However, we do have a high-tech system in place that you can count on.

When you test a template or new campaign in Email on Acid, we send it through each email client application as well as live devices. Then we stitch together screenshots of your email from each of those 100+ clients and devices and send them back to you for review.

preview of emails rendered by Email on Acid

This process is faster, more efficient, and it improves the accuracy of the testing. You get all your email previews in one place. That allows you to find and fix code that is causing problems in specific clients. If you want, you can select the clients you need to focus on to build custom testing profiles. Plus, you can also use team management features to comment and collaborate on the results.

Get much more than email previews

While previews that show you how an email renders are the foundation of our email marketing solution, we know there are other things you’ll need to catch before a new campaign hits inboxes. That’s why Sinch Email on Acid proudly provides a host of pre-send testing features:

  • Preview subject lines and preheaders with Inbox Display.
  • Ensure every subscriber can engage with your campaign when you run Accessibility checks.
  • Catch last minute typos, grammatical errors, and inappropriate language.
  • Make sure you’re not on a blocklist before sending with Deliverability checks.

Plus, you can validate links and images, use Email Analytics to track performance, and more.

We built Sinch Email on Acid to help you put your best email forward. So, try the most effective way to check email rendering and hit that send button with complete confidence.

Test Your Email First!

Make sure your email looks flawless before you send it out to your subscribers. Remember: only live email tests can guarantee fully accurate email rendering previews. With Sinch Email on Acid, you can preview your email in 100+ email clients and devices before you hit “send.” Sign up for our free trial and start testing today.

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