Email testing is challenging because emails must work across dozens of email clients, survive spam filters, render correctly with images blocked, and function properly on mobile devices. A thorough testing process catches issues before they affect recipients.
This guide covers what to test, how to test it, and how to build email testing into your development process.
What to Test
Visual Rendering
Test that emails display correctly across major email clients including Gmail (web, Android, iOS), Outlook (Windows desktop, Mac, web), Apple Mail (Mac and iOS), Yahoo Mail, and mobile clients. Check layout, fonts, colors, images, and spacing.
Content and Copy
Verify spelling and grammar. Check that personalization tokens render correctly. Ensure links point to correct URLs. Verify dynamic content displays properly. Review subject line and preheader text.
Functionality
Test all links work and go to correct destinations. Verify buttons are clickable on all devices. Check unsubscribe link functions. Test any interactive elements. Verify tracking pixels load correctly.
Deliverability
Check spam score with testing tools. Verify authentication passes (SPF, DKIM, DMARC). Test inbox placement with seed lists. Review content for spam triggers.
Accessibility
Verify alt text on images. Check color contrast meets WCAG guidelines. Test with screen readers. Ensure logical reading order. Verify plain text version is readable.
Edge Cases
Test images-blocked state. Check dark mode rendering. Verify behavior with long content. Test with different data scenarios. Check empty state handling.
Testing Tools
Rendering Preview Tools
Litmus provides previews across 90+ email clients, spam testing, link validation, and analytics. Email on Acid offers similar capabilities with client previews, code analysis, and accessibility checking. Mailtrap is great for development with fake SMTP server, HTML preview, and spam analysis.
Spam Testing
Mail-tester.com provides free spam score testing. GlockApps tests inbox placement across providers. Send emails to test accounts and check where they land.
Authentication Testing
MXToolbox validates SPF, DKIM, and DMARC records. DMARC Analyzer processes DMARC reports. dmarcian provides DMARC monitoring and analysis.
Accessibility Testing
Email on Acid includes accessibility checks. Test with VoiceOver on Mac and iOS, NVDA or JAWS on Windows. Check color contrast manually or with tools.
Testing Process
Development Testing
During development, test locally with Mailtrap or similar. Check basic rendering in browser preview. Validate HTML structure. Run through CSS inliner. Fix obvious issues before moving to comprehensive testing.
Pre-Send Testing
- Visual QA: Review in Litmus or Email on Acid across priority clients
- Link Check: Click every link, verify destinations
- Content Review: Proofread, check personalization, verify data
- Spam Check: Run spam score test, address any flags
- Authentication: Verify SPF, DKIM, DMARC will pass
- Mobile Check: Specifically test mobile rendering and usability
Test Send
Send to internal test addresses across different email clients. Verify on actual devices, not just previews. Have multiple people review. Check delivery timing and appearance.
Post-Send Monitoring
Monitor delivery metrics in real-time. Watch for bounce or complaint spikes. Check engagement rates against benchmarks. Investigate any anomalies immediately.
Testing Checklist
Content
- Subject line renders correctly in all clients
- Preheader text displays properly
- No spelling or grammar errors
- Personalization tokens replaced correctly
- Dynamic content displays accurately
- Footer information is current
Design
- Layout consistent across email clients
- Images display at correct size
- Fonts render as expected with proper fallbacks
- Colors match brand guidelines
- Mobile responsive layout works
- Dark mode rendering acceptable
Functionality
- All links work and point to correct URLs
- Buttons clickable and properly sized for mobile
- Unsubscribe link functions
- Tracking pixels load correctly
- Reply-to address is correct
Technical
- HTML validates without critical errors
- Total email size under 100KB
- Images optimized and loading fast
- Alt text on all images
- Plain text version included and readable
- Authentication will pass
Automated Testing
CI/CD Integration
Build email testing into your deployment pipeline. Run HTML validation on commit. Check for broken links automatically. Validate template syntax. Catch issues before they reach production.
Template Testing
For templated emails, test with various data scenarios including minimum data, maximum data, edge cases, and missing optional fields. Ensure templates handle all scenarios gracefully.
Regression Testing
When updating templates, test that changes do not break existing functionality. Compare before and after renders. Verify all variants still work. Check that fixes for one client do not break others.
Testing Transactional Email
Trigger Testing
Test that emails trigger at the right times. Verify correct email sends for each action. Check that timing meets user expectations. Test rate limiting prevents abuse.
Data Integration
Verify correct data populates each email. Test with edge cases like special characters, long names, and missing optional data. Check that sensitive data is not exposed inappropriately.
Delivery Verification
Confirm emails actually send when triggered. Verify delivery within acceptable timeframe. Check that failures are logged and retried. Test failure notification systems.
Common Testing Mistakes
Testing Only in One Client
What works in Gmail may break in Outlook. Always test across multiple clients.
Skipping Mobile Testing
Over 60% of opens are on mobile. Always test mobile rendering and usability.
Ignoring Dark Mode
Dark mode can dramatically change email appearance. Check how your emails look.
Not Testing with Real Data
Placeholder data may not reveal issues with real content. Test with production-like data.
Testing Only the Happy Path
Edge cases and error states need testing too. Test what happens when things go wrong.
Conclusion
Thorough email testing catches issues before they reach recipients. Build testing into your process, not as an afterthought. The investment in testing pays dividends in recipient experience and sender reputation.
GetMailer includes built-in preview and testing tools. See how your emails render across clients, check spam scores, and verify deliverability before sending.