If you’re building every email from scratch, copying old campaigns and hacking them into shape, or waiting on a developer every time you need a content change, there’s a better way.

Modular email templates let you break your emails into reusable blocks (called modules) that can be mixed, matched, and reused across campaigns. Instead of maintaining one giant HTML file or starting over each time, you build from a library of tested components.

This guide covers what modular email design looks like in practice, how to get started regardless of your team size, and how to choose the right approach for your situation. If you want a deeper explanation of the concept itself, we’ve written a complete guide to modular email templates.

What does a modular email look like?

Every email you send is made up of repeating patterns. A typical marketing email might include:

  • A header with your logo and navigation links
  • A hero section with a headline, image, and call-to-action
  • One or more content blocks (text, product cards, feature highlights)
  • A footer with unsubscribe links and legal text

In a traditional workflow, all of these live in a single HTML file. Change one thing and you risk breaking something else. Copy the file for a new campaign and you’ve just created another version to maintain.

With a modular approach, each of these sections becomes its own independent block of code. Each module is self-contained, tested, and reusable. New campaigns are assembled by choosing which modules to include and updating the content within them.

Step 1: Audit your existing emails

Before you build anything, look at what you already have. Pull up your last 10 to 20 campaigns and identify the repeating patterns.

You’ll probably find that most of your emails use the same handful of building blocks in different combinations. Common modules include:

  • Header (logo, nav links)
  • Hero image with headline
  • Text block (single column)
  • Two-column layout (image + text)
  • Product or feature card
  • Call-to-action button
  • Testimonial or quote
  • Footer (social links, unsubscribe, legal)

Write these down. This is your module inventory, and it forms the foundation of your modular system.

Step 2: Define your brand rules

Before you start splitting code, document the design rules that every module should follow. This keeps things consistent as your library grows.

At a minimum, decide on:

  • Fonts and sizes for headings, body text, and links
  • Colours for backgrounds, text, buttons, and links
  • Spacing between sections and within modules (padding, margins)
  • Button styles, including shape, size, and hover states
  • Image dimensions for hero images, thumbnails, and logos
  • Maximum width for the email layout (600px is the standard for compatibility)

If your company already has brand guidelines, pull from those. If not, this is a good time to establish them. Consistent design rules are what make modular emails feel cohesive rather than patched together.

Step 3: Break your template into modules

This is where the practical work begins. Take your best-performing email template and split it into standalone modules.

The simplest approach: HTML comment tags

If you’re a developer, a small team, or working solo, the fastest way to modularise your emails is with HTML comments. Wrap each module in a pair of comment tags that mark where it starts and ends:

<!-- MODULE: Hero -->
<table width="100%" cellpadding="0" cellspacing="0" role="presentation">
  <tr>
    <td style="padding: 40px 20px; text-align: center;">
      <h1 style="font-size: 28px; color: #1a1a1a;">
        Your Headline Here
      </h1>
      <p style="font-size: 16px; color: #555;">
        Supporting text goes here.
      </p>
      <a href="#" style="background: #2563eb; color: #fff;
        padding: 12px 24px; text-decoration: none;
        border-radius: 4px; display: inline-block;">
        Shop Now
      </a>
    </td>
  </tr>
</table>
<!-- /MODULE: Hero -->

<!-- MODULE: Two Column -->
<table width="100%" cellpadding="0" cellspacing="0" role="presentation">
  ...
</table>
<!-- /MODULE: Two Column -->

This approach gives you several benefits:

  • Easy to find and reuse. When building a new campaign, search for <!-- MODULE: Hero --> and grab the block you need.
  • Safe to rearrange. Each module is self-contained, so you can reorder them without breaking the layout.
  • Simple to maintain. Update a module once, and you have a clean reference version for future campaigns.

Store your modules in a shared folder (a Git repository works well) with one file per module. When you need to build an email, assemble it by copying the modules you need into a single file.

For larger teams: use a CMS

The comment-tag approach works well when the people building emails are comfortable with HTML. But as your team grows, or when non-technical team members need to produce campaigns independently, you’ll need a layer on top of the code.

This is where an email CMS like Modular Mail comes in. The concept is the same: your emails are made up of reusable modules. But instead of working in code, marketers use a visual interface where they select modules and fill in content fields (headlines, images, links, CTAs). The template structure stays locked, so brand consistency is enforced automatically.

This type of tool makes the most sense when:

  • Marketing teams need to build campaigns without developer involvement
  • You’re producing a high volume of emails across brands or regions
  • Brand compliance needs to be enforced at the template level, not just documented in guidelines
  • Multiple people are building emails and you need a single source of truth

Step 4: Make every module self-contained

Each module should work on its own, regardless of what sits above or below it. This is the rule that makes modular email design reliable.

In practice, that means:

  • Include all necessary styles inline. Email clients strip <head> styles inconsistently, so inline CSS is the safest approach.
  • Handle your own spacing. Each module should define its own top and bottom padding rather than relying on the module above or below it.
  • Be responsive. Every module should include its own media queries or use a fluid-width approach. Test each one individually at mobile and desktop widths.
  • Don’t depend on unreliable external assets. Host images on a reliable CDN. Broken images damage trust.

A good test: if you paste a single module into a blank HTML email, does it render correctly on its own? If yes, it’s properly self-contained.

Step 5: Test across email clients

Email rendering is notoriously inconsistent. What looks perfect in Apple Mail might break in Outlook, and Gmail strips certain styles entirely.

Test every module individually before you start combining them. Services like Litmus and Email on Acid let you preview across dozens of email clients. At a minimum, test in:

  • Gmail (web and mobile)
  • Apple Mail (macOS and iOS)
  • Outlook (Windows desktop, Outlook.com, and the new Outlook)
  • Yahoo Mail

Fix rendering issues at the module level, not the campaign level. When your module library is tested and reliable, every campaign you build from it inherits that reliability.

Step 6: Build your first campaign

With your modules built and tested, assembling a campaign becomes straightforward:

  1. Choose your modules. Pick the blocks you need from your library: a header, a hero, two content blocks, a CTA, and a footer, for example.
  2. Assemble them. If you’re working in HTML, copy the modules into a single file in the order you want. If you’re using a CMS, drag and drop.
  3. Fill in content. Update headlines, images, links, and body text within each module.
  4. Preview and test. Send a test email to yourself and check it on a couple of devices.
  5. Export and send. Copy the final HTML into your ESP (Mailchimp, Klaviyo, Salesforce, or whatever you use) and send.

The first campaign will take the longest because you’re still building your module library. But from the second campaign onwards, production time drops significantly because you’re reusing tested, approved components.

Common mistakes to avoid

Making modules too granular. A single button shouldn’t be its own module. Keep modules at the section level: a hero, a product grid, a testimonial block. If a module is so small that it never makes sense on its own, it’s probably just part of a larger module.

Skipping the testing step. It’s tempting to test the full assembled email and skip individual module testing. Don’t. Catching a rendering bug in a single module is far easier than debugging it in a complete campaign.

Not documenting your modules. Keep a simple reference that lists each module, what it’s for, and what content it expects. This is especially important when multiple people are building emails. A shared doc or a README in your repository is enough.

Forgetting about dark mode. More email clients now support dark mode, and it can drastically change how your emails look. Test each module in both light and dark mode.

Choosing the right approach for your team

The right level of tooling depends on your team and workflow:

Individual or small team with HTML skills: Start with the comment-tag approach. It’s free, flexible, and requires nothing beyond a text editor and a shared folder. You’ll get most of the benefits of modular design with zero overhead.

Growing team with mixed skill levels: Consider a lightweight template management tool. The goal is to separate content from code so that less technical team members can contribute to campaigns without risking the underlying structure.

Large team, agency, or enterprise: A dedicated email CMS gives you locked templates, content fields, role-based access, and ESP-agnostic export. This is where the investment pays off at scale, allowing marketing teams to build campaigns in minutes rather than days without risking brand consistency.

Whatever approach you choose, the principles are the same: break your emails into self-contained, reusable modules, test them thoroughly, and build campaigns by assembling proven components. Start simple, and add tooling as your needs grow.