You’ve done the hard part. The copy is tight. The design looks beautiful. You hit send, and pff: a technical issue kills all the effort. Because the button’s broken on Outlook, or because the email landed in spam, or is illegible on mobile.
This happens more than you think. Statistics back this up: 35.1% of marketers say their biggest email design and development challenge is inconsistent rendering, while 22.4% say they face accessibility issues, and 22.8% have issues with coding.
And it’s not just ecommerce or retail: B2B teams sending onboarding emails, invoices, or renewal reminders face the same rendering risks. One bad email can hurt trust or cause confusion right at a critical touchpoint.
Email clients are picky. Gmail, Outlook, Apple Mail: they all render code differently. A broken CTA or misaligned layout can mean lost clicks, missed revenue, and a loss of trust in the brand, which can lead to some recipients clicking on the dreaded, "mark as spam" button.
It doesn’t have to do so, though. In this post, we’ll walk through what to check, how to test across devices, and how to build a repeatable workflow that saves you from those misses.
The essential email testing checklist
Before you hit send, run your email through this essential checklist. It’s short, skimmable, and covers the most common failure points that derail campaigns.
- Subject line and preview text verification: Double-check that your subject line and preview text are displaying as intended across major inboxes. Avoid cutoff text, filler like "Lorem ipsum," or placeholders that weren’t replaced. Test on both desktop and mobile views.
- Alt text and image rendering: Ensure images have meaningful alt text. For images that are just decorative and contain no content (like divider images, for instance), it's best to have the alt text tag in there but leave the attribute blank. This also smooths the screen reader experience. This matters for accessibility and also for users who have images turned off by default. Load the email in different clients to confirm that all images display correctly and aren’t broken or distorted.
- CTA visibility and functionality: Make sure your primary call-to-action stands out visually and is clickable in all environments. Pay special attention to Outlook, where buttons often misalign or break. Test tap targets on mobile for usability.
- Link validation: Click every link manually. Confirm that UTM tracking parameters are attached where needed, and that there are no redirects leading to 404 errors or outdated pages. Beefree's Smart Check feature verifies all links are valid (not broken) and point to the correct destination.
- Font compatibility fallback check: Stick to system fonts or use proper fallback options if you're using custom fonts. Test the email in clients that don’t support custom fonts to ensure legibility and layout integrity.
- Mobile responsiveness: Preview the email on at least one iOS and one Android device. Check that the layout stacks correctly, text remains readable, and images scale as expected. Avoid horizontal scrolling at all costs.
- Dark mode rendering: Open the email in dark mode across common clients like Apple Mail, Gmail, and Outlook. Ensure logos, icons, and background colors don't invert in ways that ruin readability or branding.
- Accessibility basics: Verify that your color contrast meets WCAG standards, especially for text over backgrounds. Use semantic HTML where possible and test with a screen reader to confirm your content reads in the correct order with descriptive labels.
- Inbox placement and spam score: Run your email through a spam-check tool to catch any red flags. Confirm your domain has valid SPF, DKIM, and DMARC records. Do a live test send to a seed list with accounts across Gmail, Outlook, and Apple Mail, especially if your emails are triggered by systems like CRMs, ERPs, or AI quoting software, to check for inbox placement.
Device & Client Previews: How to Test Across Environments
An email that looks perfect in Gmail might fall apart in Outlook. Or display fine on desktop but break on mobile. That’s because different email clients interpret the same code in different ways, and not always in your favor.
In fact, there are over 50 major email clients in use today. Each one has its quirks. Outlook may strip padding. Gmail might ignore custom fonts. Apple Mail tends to render beautifully, but only if everything else is clean. Add dark mode and mobile to the mix, and testing across devices becomes essential, not optional.
So, what should you preview? Here is a good starting point:
- Desktop (Gmail, Outlook, Apple Mail)
- Mobile apps (Gmail app on Android and iOS, Apple Mail, Outlook mobile)
- Webmail (Yahoo Mail, AOL, Outlook.com)
- Light mode and dark mode versions for each
Test both plain text and HTML versions where applicable. If you don’t want to test manually across dozens of devices, use a rendering tool. Popular options include:
- Inbox Monster: Offers previews for every modern email client (and includes dark mode!).
- Email on Acid: Similar feature set with built-in optimization tips.
- Mailtrap: Great for staging environments and safe test sends.
Many ESPs (like Mailchimp, Campaign Monitor, or HubSpot) also offer basic preview features. Take advantage of them during the final QA.
And if you don’t have access to paid tools, at the very least, send test emails to real accounts you control:
- A Gmail address (mobile and desktop)
- An Outlook.com or Hotmail address
- An Apple Mail inbox
- One older Android device
This covers most of the edge cases you’ll run into. Watch out for these common rendering issues while you’re at it:
- Button padding or alignment issues in Outlook
- Images not loading in Gmail unless enabled
- Font fallbacks not kicking in properly
- Stretched or collapsed layouts on narrow mobile screens
- Background colors disappearing in dark mode
Catch these before your users do. That’s the whole point of previewing.
A repeatable email testing routine
The best email teams don’t test in panic mode. They follow a routine. One that’s baked into their process, not slapped on at the end.
Here’s a simple, repeatable testing workflow you can adapt to any team or toolset.
Step 1: Final content and design check
Once your email is written and designed, review the final content in context. Check for tone, clarity, and formatting. Confirm that placeholder text is removed, images are optimized, and copy matches your brand voice.
Step 2: Code and layout review
If the email is coded, validate the HTML and CSS. Look for nested tables, inline styles, and media queries for responsiveness. If you're using a drag-and-drop builder, double-check that the exported HTML isn’t bloated or broken.
Step 3: Internal test send
Send a version to yourself and your team. View it across:
- Desktop clients like Outlook and Gmail
- Mobile apps on iOS and Android
- At least one webmail client like Outlook.com
Use this as a gut check: Does it look good? Does it feel right?
Step 4: Device and client preview
Use a tool like Litmus or Email on Acid to generate previews across common environments. Focus on key clients used by your audience. Look for rendering issues, broken layouts, or dark mode mishaps.
Step 5: Functional QA
Click every single link. Test buttons. Fill out forms (if applicable). Validate alt text by disabling images. Run the email through a spam check and confirm deliverability settings are in place.
Step 6: Approval
Once the test version passes all checks, route it for approval. Keep the process simple: email threads or shared docs work fine. Make sure stakeholders know exactly what they’re reviewing.
Step 7: Send to a seed list
Do a final send to a small group of internal addresses (your seed list) using your ESP. Monitor delivery and rendering in live inboxes. If anything looks off, now’s your chance to fix it.
Step 8: Schedule or send
Only now is it ready to go out. Schedule your send or hit publish. And if your ESP supports A/B testing, this is the moment to set that up too.
This routine doesn’t need to take hours. With the right setup, you can run through it in under 20 minutes. And it’ll save you from headaches down the line.
Common email testing mistakes to avoid
Even experienced teams slip up. But most email testing mistakes are easy to prevent once you know what to watch for. Here are some of the most common ones that derail otherwise great campaigns.
1. Only testing in one email client
Gmail is popular, but it's not everything. If you're only testing in Gmail on desktop, you're ignoring how your email looks for Outlook users, Apple Mail users, and nearly everyone on mobile. Always test across a mix of platforms.
2. Skipping mobile previews
A large chunk of your audience reads emails on their phones. If your email isn’t mobile-friendly—if text is too small, images are too wide, or buttons are hard to tap—you’re losing conversions. Always check the mobile layout.
3. Ignoring dark mode
Dark mode isn’t just an email design trend. It’s the default for many users. If you haven’t tested your email in dark mode, logos might disappear, background colors might flip, and your text could become unreadable.
4. Forgetting to test personalization
Using first names or dynamic content? Make sure fallback values are set and rendering correctly. Broken personalization tags are a fast way to make an email look sloppy or robotic.
5. Skipping alt text
No alt text means your email loses context if images don’t load. It’s also an accessibility fail. Every image, especially those tied to CTAs, needs clear, concise alt text.
6. Overlooking broken links or buttons
It happens all the time: a typo in a URL, a button that doesn’t go anywhere, or a link that leads to the wrong landing page. Click every link manually during QA. No exceptions.
7. Relying too much on images
If your email is 90% images, and a client blocks images by default, your message is gone. Use real HTML text wherever possible. Save images for visual support, not content delivery.
8. Not running spam or deliverability checks
Your email might look great, but if it never hits the inbox, none of it matters. Always run a spam score check and make sure your SPF, DKIM, and DMARC settings are valid. Avoiding these mistakes doesn’t take much time. But it makes all the difference between an email that gets ignored and one that performs.
Wrapping up
Most email mistakes aren't about bad content or poor design. They're about skipping the final checks.
When you build testing into your workflow—not just at the end, but throughout—you avoid the common traps. You catch broken buttons. You spot mobile layout issues. You fix those rendering quirks before they go out to thousands of people.
That’s how you go from sending emails that are “fine” to ones that actually perform. And yes, email testing isn’t glamorous. But it’s what separates the pros from everyone else.
