How to design high-converting HTML email templates

A great HTML email template is more than colours and code. Done right, it’s a repeatable framework that drives clicks and revenue — not just opens.

Whether you’re a marketer who writes copy or a developer who codes tables for Outlook, this guide will help you design templates that are easy to reuse, look good everywhere, and give your campaigns the best chance to convert.

1. Start with a single-column or hybrid layout

HTML email clients are notoriously unpredictable. Simple, single-column layouts are easier to make responsive and keep your message focused.

When you need more visual interest, use a hybrid: a single-column header, a multi-column content block for products or features, then single-column again for your CTA.

Checklist:

  • Table-based structure (for Outlook compatibility)
  • Responsive design using inline CSS and @media queries
  • Minimum 14px body text for readability

2. Lock your brand styles in the template

In high-performing teams, design decisions aren’t made mid-build. The template itself enforces the brand: colours, fonts, padding and button styles are baked in.

Why it matters:

  • Guarantees consistency across campaigns
  • Prevents “one-off” style changes that dilute brand recognition
  • Speeds up builds because no one’s debating colours each time

If your team edits HTML directly, create a CSS section at the top for all brand tokens and reuse it across templates.

3. Lead with one clear goal per email

Your template should guide the reader to take a single action. That might be a purchase, booking a demo, or reading an article.

Best practices:

  • Make the primary CTA button stand out (colour contrast, size, placement)
  • Keep copy above the fold concise and action-oriented
  • Repeat the CTA at the bottom for long emails

4. Use visuals that load fast and add context

Slow-loading images cost clicks. Optimise images for size (aim under 200KB) and always include descriptive alt text.

Tips:

  • Use real product shots or context images — avoid generic stock
  • Host images on a reliable CDN
  • Consider using live text for headlines instead of embedding them in images

5. Make it accessible

Accessibility isn’t just compliance — it’s good UX.

  • Use semantic HTML (<h1>, <h2>, <p>) for screen readers
  • Ensure colour contrast ratios meet WCAG AA
  • Provide alt text for every image
  • Avoid text embedded in images where possible

6. Test before you send

Even the best-coded template can break in an unfamiliar client.

Minimum test matrix:

  • Apple Mail, Gmail, Outlook desktop, Outlook web, iOS Mail, Android Gmail
  • Dark mode on mobile and desktop
  • Link click tracking and CTA button rendering

Tools like Litmus or Email on Acid will save hours of manual testing.

7. Reuse and iterate

The fastest teams don’t reinvent their templates. They reuse modules: hero, product grid, testimonial, footer.

With a modular system, you can:

  • Swap modules in/out to suit the campaign
  • Keep HTML consistent across sends
  • Roll out brand updates globally by editing a single module

Quick HTML template checklist

  • Single or hybrid column layout
  • Locked brand tokens in CSS
  • One clear CTA
  • Optimised images with alt text
  • Accessible colour contrast
  • Tested in major clients
  • Built from reusable modules

Build it once, use it forever

High-converting HTML email templates aren’t just well-designed — they’re governed by a repeatable system.

If you want a modular, locked-down HTML template that your whole team can use — without ever touching code — try Modular Mail. We set up your template system once, and you can export clean, responsive HTML for any ESP.

Start your free trial or book a template build to get started.