How to leverage email inbox preview testing for seamless rendering and increased engagement

Email rendering is the process by which an email message is displayed on the recipient’s device through their chosen email client, with each client using different rendering engines that affect how the email’s HTML and design elements appear. Because not all email clients and devices render emails the same way, how your emails load and function directly impacts user experience, engagement, and deliverability. 

Email rendering issues can make a message look broken across different devices and clients. With an email inbox preview tool, you can test how your email renders in Gmail, Outlook, iPhone, Pixel, and more for a responsive, consistent experience for every subscriber. 

Email rendering across email clients and devices goes beyond “does it look good”. How your emails load and function affects user experience and engagement, which impacts your deliverability. The trouble is, not all device types and email clients render in the same way.

So, how can you be sure that an email design that looks perfect in your builder will render correctly in Outlook? And how do you avoid common Gmail or iPhone email rendering issues that can break your layout on mobile? Email rendering testing and preview tools give you the visibility you need before hitting send. 

In this post, we’ll fill you in on how email preview can help overcome rendering roadblocks and show you how you can use email preview tools to test rendering before you send. 

Not to be confused with email preview text, the copy that comes up next to the subject in your inbox, an email preview is a view of how an email message will look in the inbox before it is sent – regardless of what device, email client, or operating system your recipients use to view it. The question is, do you need to preview your messages?

The answer is easy when you consider the statistics. When it comes to email, human attention span is shrinking, from about 13 seconds in 2018 to 9 seconds in 2022 – soon it’ll be shorter than the five-second food rule. If your message suffers from email rendering issue – like broken images, Outlook formatting errors, or mobile layouts that don’t fit the screen – readers will tune out even faster. Most people spend less time with a poorly rendered email than they do thinking about eating that tasty morsel that just fell off their plate.

Looks matter. Even for email. Even in email. Think of an email preview tool as the mirror you check before heading out the door: a final chance to catch mistakes before sending. Beyond peace of mind, email previews offer two key benefits: they help identify email rendering issues across clients and they ensure a consistent, responsive design for every subscriber.

Since we’re talking about the five-second rule, we’ll keep the etiquette lesson going and take a page from the southern mother’s handbook. Email previewing tests if your messages will sit pretty and act nice in the inbox. It’s not all about looks, your messages have to behave and arrive at the inbox in working order.

Before we talk about why email previewing is important for rendering, and what some of the industry challenges are, we need to understand a bit more about email responsiveness. 

Email responsiveness is whether or not a message is compatible visually across devices, email clients, and operating systems, and if it is compatible functionally. Do all the buttons work? Do the links register? If you’ve built an interactive email, is it universally accessible?

Now that we’ve brushed up on email rendering, here’s how email preview fits in. Not all devices and email clients render emails with the same standards. It’s your job as the sender to develop an email that is compatible with them all. (We were tempted to put a Lord of the Rings reference here, but we’ll hold it in.) 

Since well-rendered emails speak to consistency, email previewing has to be a multi-perspective practice.

In other words, it’s essential to preview your emails across multiple devices and clients to catch potential email rendering issues. When most people think of email clients, the big names like Apple Mail, Gmail, and Microsoft Outlook come to mind. But within those platforms are hundreds of versions and screen experiences, each with the potential to display your message differently making email rendering testing a must.

Now things are starting to get a bit more complex.

Email rendering across multiple email clients is a constant challenge for businesses. With a multitude of email clients and devices in use today, senders must navigate the intricacies of HTML and CSS compatibility, responsive design, and rendering inconsistencies to ensure emails are received and displayed correctly across all platforms. Email preview tools can help overcome these challenges by testing emails before they are sent to avoid broken elements that can harm brand image, downgrade user experience, and impact engagement and conversions.

Kate Nowrouzi VP of Deliverability at Sinch Mailgun

The biggest challenge of email rendering is that there is no standardization among email clients. None. Zero. Zilch. In fact, each client has its own special email rendering engine that controls how your sent messages are displayed. This means that if you test your emails for Apple, they may not look the same in Gmail. But it actually goes deeper. 

Each major provider, such as Gmail, actually includes a series of different email clients for web, mobile, and desktop views. On top of that, there are further variations depending on the operating system, whether it’s Android or iPhone. These differences are a common cause of Gmail email rendering issues or iPhone email rendering issues. Here’s an example: 

Since email clients aren’t standardized, it’s best to build messages with responsive designs that are capable of adapting to different rendering engines and standards. We linked to our best practices earlier in this post but here are a few key tips: 

• Adopting mobile-first design principles that work within the boundaries of smaller screens
• Using media queries and fluid layouts that are adaptable
• Optimizing images for different screen sizes

Sounds too complicated? Check out our responsive email templates and use them to build your own!

The email rendering rabbit hole is a long, long tunnel. The best way to navigate it is to simplify your sending with best practices and email previewing before you send.

Email rendering is tricky because every client and device displays messages differently. Outlook uses Word’s rendering engine, while Gmail and Apple Mail rely on WebKit or Blink. HTML and CSS support varies across clients, and operating systems, from iOS and Android to Windows and Mac, affect layouts on desktop, tablet, and mobile. Add user settings like dark mode, image blocking, or screen readers, plus code-modify. 

Even well-designed emails can run into rendering problems. Common issues include broken layouts, misaligned elements, unsupported media like GIFs or videos, background image failures, and buttons or CTAs that don’t display correctly. Email rendering testing tools help catch these problems before your message reaches the inbox. 

Now we’ll cut into the meat of email inbox preview testing and the impact it has on your deliverability.

The number one benefit to an email that renders perfectly across clients and devices is in an increased engagement rate. Correctly rendered emails support user interaction and click-through because all of the elements are functioning and visible to the user.

Testing responsiveness and ensuring rendering of images, fonts, layouts, hyperlinks, etc., means you are sending compatible messages that can adapt to different rendering engines. Correctly rendered emails are less likely to be flagged as spam, and also more likely to drive positive engagement – a great sign for mailbox providers that your email is legitimate and wanted.

Utilizing online testing platforms to preview emails on different devices and across a large volume of email clients allows you to troubleshoot and resolve any rendering issues prior to sending your campaigns, protecting your deliverability from the negative impact of broken emails.

Ok, so now that we’ve convinced you that previewing your emails is in your best interest, how do you do it?

There are plenty of email preview services available, but one thing is certain: there’s no simple way to manually test your messages across every device and client. Without a tool, you’d need an arsenal of hardware: dozens of phones, tablets, and computers running different operating systems, plus a team to sift through the sea of test emails. That’s why dedicated email rendering testing tools are essential. 

Trust us, not only do you need the support of a platform, you want it.

Email previewing comes with a wide range of capabilities. To get the most value, look for an email rendering testing tool that includes these key features. Mailgun combines them all to help you identify rendering issues, ensure responsive design and maximize subscriber engagement. 

• Email clients – there are a lot of them: A top email preview tool should let you test across the widest range of devices and clients to catch any rendering issues. With Mailgun, you can preview your emails in over 100 clients across web, mobile, and desktop, ensuring consistent email rendering no matter where your subscribers open them. 
• Eye-catching emails grab your recipients’ attention, and email previews can help make that happen: A good email preview tool lets you test more than just the message body. Make sure you can see how your subject lines, sender name, and pre-header text render across Gmail, Outlook, and iPhone to avoid email rendering issues before your message hits the inbox. 
• Optimize your emails for user preferences: Beyond your custom CSS and HTML designs, recipients can control how emails appear on their devices. Dark mode is a prime example. Over 82% of users engage with it in some form. If your messages aren’t optimized for dark mode, you risk email rendering issues and poor engagement. Make sure your email preview tool lets you test how your emails display in both light and dark modes. 

Mailgun offers this and much more. If you want to learn more about the Email Preview tool and its features, check out our product page.

Don’t risk damaging your brand with emails that don’t render properly. First impressions matter, and an email preview acts as your second opinion. Even the best-designed messages can run into email rendering issues if they aren’t tested. With so many variations across email clients, devices, and operating systems, email rendering testing is essential to ensure your message looks perfect for every recipient. 

That’s why responsive emails are the key to rendering and email inbox preview testing is the secret to guaranteeing responsive emails. Just because it looks good in your environment doesn’t mean it looks good on the mobile device in the palm of your biggest client’s hand.

Email preview is effective but also simple. Try out our solution and experience how previewing your emails fits into your larger deliverability strategy.

Author: Kate Nowrouzi Kate Nowrouzi is the VP of Deliverability at Sinch Mailgun. She is our in-house deliverability pro and product strategist with over 20 years experience in email & anti-spam technologies. She writes about deliverability, brings you best practices, and shows you the impact of email on your business.