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Cerberus A few simple, but solid patterns for responsive HTML emails. Even in Outlook and Gmail.

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Cerberus -
Between mobile, Gmail, and Outlook, HTML email is a three-headed dog from hell.


Coding regular emails is hard enough by itself. Making them responsive shouldn’t add to the headache. A few simple, but solid patterns are all that’s needed to optimize emails for small screens.

That’s what Cerberus is.

It’s just a few responsive email patterns that go a long way. The code blocks are compartmentalized so they may be used, removed, combined, and nested to build an email.

Each template contains code comments and has good support among popular email clients.

I wrote a blog post that goes into more detail on why I made this in the first place. Cerberus is Responsive Email XX’s successor.

Things To Know

  • Cerberus is a small collection layout patterns for HTML email. The code is meant to be edited, adapted, and built upon.
  • The code is compartmentalized and annotated in an effort to explain what’s happening so you can add, edit, and remove code with some confidence.
  • This has been tested in all “popular” email clients, but not every email client out there. More on that here.

The Templates

As the layout narrows, the email content reflows and resizes gracefully.

Fluid Template

Good for simple layouts such as transactional and single column emails.

This template focuses on a fluid layout that sizes itself using percentage-based widths to shrink horizontally on narrow screens. This email layout does not reconfigure at different screen sizes.

If you want a basic template to handle rich text and images, this is a good baseline.

The email layout changes at breakpoints using media queries.

Responsive Template

Good for more complicated, shape-shifting email layouts that work on some mobile clients.

This template uses media queries to reconfigure the layout for different screen sizes for email clients that support media queries. However, mobile clients that don’t support media queries or the <style> tag will display a shrunk version of the desktop layout instead. This applies to some versions of Gmail (still) and Yahoo, as well as a number of international email clients (more info on that here).

If you’re already comfortable with media queries, the learning curve is relatively low. If total device coverage isn’t required, you can create a responsive email the same way you create a responsive website.

The email layout stacks without media queries.

Hybrid Template

This template uses a hybrid approach to reconfigure the layout for different screen sizes for email clients regardless of media query support. At its core, it uses max-width and min-width to impose rigid baselines (allowing some movement) and imposes a fixed, wide width for Outlook who is shackled to desktop anyway. Once a mobile-friendly baseline is set, media queries progressively enhance the email further in clients that support it.

If you have some email design experience, this template optimizes every popular email client. All the extra Outlook code can make these templates quite large and your maths have to be spot on for multi-column layouts.


Templates in the archived-versions folder are not currently being maintained and should be considered unsupported and deprecated. They are kept around for historical purposes. 💫

Client Support

Cerberus is tested in the most popular email clients as reported by Litmus and my own email campaigns. I’ve focused on the following clients:

  • Desktop
  • Outlook 2000/02/03/07/10/13/16 (Windows)
  • Windows 10 Mail
  • Outlook 2011/16 (Mac)
  • Apple Mail 9/10
  • Thunderbird
  • Web (Chrome, FF, IE)
  • Gmail (IMAP, Business
  • Outlook.com
  • Yahoo
  • Aol
  • Office 365 Web
  • Comcast
  • Web.de
  • GMX.de
  • freenet.de
  • T-Online.de
  • Mail.ru
  • Terra Mail
  • Mobile Apps
  • iOS Mail (iPhone 5 and up, iPad, iPad Mini)
  • Gmail (iOS+Android, all account types)
  • Google Inbox (iOS)
  • Mail (Android 6.0)
  • Yahoo (iOS)
  • Outlook (iOS)
  • Alto Mail (iOS)

When I say “tested”, I mean “email doesn’t fall apart”. I don’t mean "Everything is pixel perfect in Outlook" or “I found a way to make media queries work everywhere.” They don’t.

There are multiple versions of Gmail. Cerberus works pretty well in all of them. Rémi Parmentier created an excellent graphic explaining Gmail’s capabilities in this article.

Any client not listed above should be considered untested. If you feel I’ve left out a popular email client or can suggest a non-destabilizing fix for one, please submit an issue!

For what it’s worth, Litmus (who does test every email client) includes Cerberus in its Email Builder, so there’s that.

Known Issues

Not necessarily a bug with the code in this repo, but a few things that could trip you up.

  • Some ESPs don’t like URLs in HTML comments (example issue). In this case, you can remove the URLs or even the entire HTML comment.

A Word on CSS Inliners

I recommend against using a CSS inliners with Cerberus. Here’s why:

  • Cerberus is supposed to be simple and should not require a dependency like a CSS inliner.
  • The placement of Cerberus’s CSS is already optimized. The CSS in the <head> is meant only for email clients that parse CSS in this location. It doesn’t need to be inlined.
  • There are some CSS selectors like :hover that don’t inline so well and throw errors in some CSS inliners.
  • Inlining leads to code bloat. Not only does this impact download speeds, but some email clients like Gmail and iOS Outlook truncate messages after they exceed a certain file size.

I’m a fan of using snippets, available most code editors. I understand CSS inliners help many folks, but if you use one with Cerberus, please do so at your own risk. I recommend Lee Munroe’s CSS inliner and hear good things about Roadie.


If you would like to help, please @reply me on Twitter or open an issue to discuss your idea. I’m forever interested in reducing the entropy of this code. I’m most interested in:

  • Fixing existing code that’s broken.
  • Reducing the amount of code in existing patterns.
  • Improving the documentation.

Please be mindful there are three templates that share a lot of code. Many changes apply to all three.

Please branch off the main branch instead of master.


Hello! I’m Ted Goas, the core author and maintainer. I’m a designer & front-end developer working on websites, web apps, and HTML emails. And I enjoy talking shop on Twitter.