Ever spent hours crafting a beautiful email with engaging copy, only to find out your recipients see colour inversion problems, blocked images, unreadable text, or broken logos? Your newsletter looks flawless in Apple Mail, but falls apart in Outlook. And Gmail? It might just ignore your fancy HTML animations altogether. The frustrating truth: every inbox plays by its own rules.
As a marketer, you need to think about it all: the devices your audience uses, the quirks of their email clients, screen sizes, whether images load or get blocked, and even how personalisation tags behave differently across platforms. The email design process is just the first step. The next step, and the most challenging, is to ensure that your email renders well.
Email rendering refers to how your email is viewed across various email clients and devices, as every platform follows different rules for how it displays emails. Here, we will explain what can impact your emails, how to ensure that your content works on different devices and platforms, and how to use modular email design to send brand-consistent content and save time on testing.
The email rendering process: What can impact your emails?
Email clients don’t have a universal rendering standard, making it challenging to ensure your newsletters look as intended across all inboxes. Rendering issues are like surprise guests crashing your email party—best to spot them before the invites go out.
Here are the top factors affecting email rendering that you should always test before your campaign launch:
- Desktop and mobile
According to statistics, email opens from mobile devices range from 26% to 78%, depending on your target audience and services you provide, making responsive design a must-have. However, not all email clients interpret media queries consistently.
For example, two-column layouts should ideally change into one-column for mobile devices, but in some clients, that doesn’t happen, leading to poor readability. That’s why it’s essential to opt for table-based structures with percentage widths (width=”100%”) and check that your HTML and CSS don’t have any errors.
Here is an example of a desktop email layout:
And here is an example of a properly rendered one-column email layout for mobile devices:
(Source: Stripo template)
- Email client differences
Each email client has its quirks. What looks great in one might look broken in another. Gmail, Apple Mail, Outlook… they all speak slightly different ‘languages’ when it comes to HTML and CSS. If your recipients use the Gmail app on Android but with a non-Google account—a setup called ‘GANGA’—you might face unexpected rendering quirks. Outlook for Windows doesn’t have enough support for modern CSS (rounded corners in the email or background images, if you don’t use VML).
Depending on your subscribers’ inbox settings and their preferred email clients, your email may appear completely different from the one you designed. That’s why testing across platforms is not optional—it’s essential.
- Dark and light modes
Did you know that around 82% of smartphone users prefer dark mode? It’s crucial to test your emails for dark mode—if your logos or images have a transparent background, they may blend into the dark background of the inboxes. Some email clients automatically invert colours in dark mode, affecting readability due to a poor colour contrast.
(Source: Stripo template)
- Images on vs. off
Building your emails by relying on images alone can lead to your content looking like a blank canvas in inboxes. Sometimes email clients block images by default, or they don’t display because of large file sizes. Therefore, you must make sure to present the important information in real text and not just in a banner, as well as equip your visuals with descriptive alt text and compress images for faster loading. You can also disable images during testing to check if your email is still understandable without them.
Here is how an email with images turned off looks like:
(Source: Email from Clinique UK)
As you can see, all the important information is presented in real text, making an email understandable even without images.
- Merge tags
Personalisation in email marketing can raise your open rates and establish deeper audience relationships, but dynamic content powered by merge tags (such as recipients’ names or locations) can easily break if you don’t test them properly. You can face fallback issues because of a single typo or an unsupported tag.
- Accessibility
Your recipients are real people, not just email addresses in your email list, and real people have to live with all kinds of disabilities, ranging from vision problems and photosensitive epilepsy to motor impairments and dyslexia. Common rendering issues include missing alt texts, poor colour contrast, and improper structure for screen readers, which may create barriers for some recipients. Make it easier for all people to interact with your emails.
- АМР, kinetic emails, and restrained HTML5
There are two ways to create interactive emails: AMP for Email and HTML5 & CSS3. AMP emails are wonderful if your audience is using Gmail or Yahoo. But they’re useless in Outlook or Apple Mail. If you’re going interactive, make sure you build smart fallbacks that work where AMP doesn’t.
A fallback is a version of the interactive element that displays in email clients that don’t support interactivity. Fallbacks ensure your emails stay functional and understandable even without interactivity.
(Source: Email from Litmus)
AMP and kinetic elements, such as the rollover effect or embedded forms, can boost engagement, but they require AMP and HTML5 & CSS3 fallback to ensure that interactivity works for the majority of your recipients.
How to ensure your emails work, on every device, in every inbox
Even though the diversity of email clients and devices is a huge issue, it’s still not the main challenge to solve. It’s the time it takes to spot, fix, and re-check an issue. And while we can’t control that complexity, we can control how fast we detect errors and fix them. Keep your feedback loop short: spot, fix, recheck, repeat.
Now that we have looked at the key factors that affect email rendering, let’s focus on the different testing methods, from quick visual checks to more detailed rendering previews. This approach will help you detect most issues quickly so that you spend more time only when it’s really needed.
- Testing emails in the editor (WYSIWYG)
This is the first and fastest line of defence. What you see is what you get (WYSIWYG) editors allow you to spot layout issues as you design, making this a quick way to catch and fix any errors as you build your emails. Padding issues, broken layouts, or off-brand colours—you will be able to detect these issues immediately. These editors show what your newsletter will look like in the majority of popular email clients. Not all platforms offer this, but it’s a powerful tool when available.
- Preview mode
You can also switch to preview mode in your editor for quick visual checks to understand how your email is viewed on desktop computers and mobile phones. It’s not always enough, though, and you will need to jump back and forth from preview mode for edits. If you don’t spot any rendering issues in preview mode, you can move on to the next step of the testing process.
- Inbox testing
Cooperate with your colleagues and send a test email to as many devices and email clients as you can (don’t forget to include both light and dark modes). Remember to test an email in Gmail with AMP on and off, Apple Mail for kinetic email testing, and Outlook to avoid container or structure background issues and menu items losing their styles.
- Testing tools
This final step is ideal for full coverage of the environment. With tools such as Email on Acid or Litmus, you can preview what your newsletter will look like across 100+ email clients and devices. These tools are integrated with some email building platforms, making the testing process even faster.
Every new email requires a repeat of this multi-step process—you build a new email, test it through each of these testing methods, and fix the issues you detect. It’s time-consuming but worth it. If your workflow is structured well, it doesn’t have to be overwhelming.
Modular email design: Your shortcut to faster testing and consistent emails
Modular email design is a great way to save time and effort as you don’t have to build each email from scratch. Instead, you create reusable content blocks—modules—for the email elements that you use most often (e.g., headers, footers, menu, product cards, etc.). Then, you can test these modules once and reuse them across your future email campaigns without worrying about breaking design or functionality.
Even when you update content inside a module (e.g., the copy, images, or links), core properties, such as colour contrast, font size, and accessibility settings, stay the same. When you need to create a new module, the testing process will be much faster, as you are not starting from scratch—all of your other modules have passed all the necessary rendering checks.
This approach significantly reduces the need for time-consuming, full-scale email testing. Elements such as merge tags, dynamic content, and accessibility settings will stay unchanged and won’t require retesting unless you want to change the design.
As a result, with modules, you can test just the final version of the email instead of each block and reduce the number of edits, as you have already tested your modules once and know they work flawlessly. That means fewer complex checks and more confidence in every newsletter you send.
Wrapping up
Email rendering is essential to confirm that your emails are consistent and functional, no matter where they are opened. From font substitutions to colour inversion in dark mode, unanticipated changes to the appearance of your emails can impact subscriber engagement. Proper email rendering leads to improved engagement, fewer spam complaints, and higher conversions.
You’ve worked hard on your email, don’t let rendering glitches undo it. Test smart, test often, and stay ahead of the challenges so your audience sees what you intended.
Have you ever faced rendering issues during your email marketing campaigns? We’d love to hear how you solved these challenges!
Want to deepen your email design skills?
If this article sparked a few lightbulb moments, you’ll love the CPD-Certfied Foundation Email Design Excellence course inside the Holistic Email Academy. Co-tutored by Dmytro, it walks you through the fundamentals of building emails that render beautifully, convert reliably, and save you hours in production time.
It’s the perfect next step for marketers who want to level up their design workflow and confidently create emails that look great everywhere.
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