Definition
Browser rendering describes how a web browser interprets and displays the HTML and CSS of an email viewed through a web-based email client. Unlike desktop or mobile email apps, browser-rendered emails are subject to the rendering engine of the specific browser (Blink for Chrome, WebKit for Safari, Gecko for Firefox) combined with the email client's own CSS transformations.
This creates a complex rendering environment where an email may look different depending on the browser, the email client, and their interaction.
Rendering Engines and Email Clients
| Browser | Rendering Engine | Affected Email Clients |
|---|---|---|
| Chrome | Blink | Gmail (Chrome), Yahoo Mail (Chrome) |
| Safari | WebKit | Apple iCloud Mail, Gmail (Safari) |
| Firefox | Gecko | Gmail (Firefox), Yahoo Mail (Firefox) |
| Edge | Blink (Chromium) | Outlook.com, Office 365 (browser) |
Common Browser Rendering Differences
- CSS support: Chrome supports more modern CSS than Firefox in email contexts
- Font rendering: Different browsers render web fonts and system fonts differently
- Image handling: Each browser has different default image loading behaviours
- Interactive elements: AMP for Email and hover effects vary by browser support
- Dark mode: Each browser/email client combination handles dark mode colour inversion differently
- Responsive design: Media query support and behaviour varies across browsers
Testing Browser Rendering
- Test across browsers: Preview emails in Chrome, Safari, Firefox, and Edge
- Use rendering tools: Litmus and Email on Acid simulate browser rendering
- Check browser-specific quirks: Some browsers have known issues with specific CSS properties
- Test on different OS: Rendering differs between macOS and Windows for the same browser
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Related Glossary Terms
Above the Fold in Email
Above the fold in email refers to the content visible to a recipient before they scroll, a critical area for first impressions and primary calls to action.
Accessible CTA (Email)
An accessible CTA is a button or link coded with sufficient colour contrast, visible focus states, descriptive screen-reader text, and a minimum touch target of 44×44 pixels.
Adaptive Design
Adaptive design in email uses predefined layouts that adjust to specific device or client widths, rather than fluidly resizing to every possible screen.
AI-Generated Content in Email
AI-generated content in email is copy, images, code or subject lines produced by artificial intelligence tools to speed up campaign production and testing.
Alt Text
Alt text is the written alternative to an image in an email, displayed when images are blocked, slow to load, or consumed by screen readers.
Autoplay Video in Email
Autoplay video in email refers to the limited ability to play video content automatically when an email is opened, using specific client-supported techniques.
Frequently Asked Questions
Chrome (Blink) generally offers the broadest CSS support and most predictable rendering. Safari (WebKit) has stronger standards compliance but more limitations. Firefox offers good standards support but has a smaller email client user base.
Yes. Web-based email (Gmail, Yahoo, Outlook.com) accounts for approximately 60-70% of email opens, making browser rendering the most important consideration for email design. Mobile apps and desktop clients make up the remainder.
Optimise for the browsers your audience uses by checking your analytics for browser-level open data. If unavailable, prioritise Chrome (most popular) and Safari (significant market share among mobile and Mac users).