Email Coding Guidelines

Where I share my coding principles for HTML emails.

Last week I attended the EMday conference near Paris and shared some of my best practices for coding HTML emails. I wrote a full document and it’s available on GitHub for anyone to share, contribute and adapt to your own needs. This is heavily inspired by some popular web coding guidelines, like @mdo’s Code Guide and Stack Overflow’s Email Design Best Practices.

The goal of this document is to establish principles that anyone can apply to code modern, well supported and accessible HTML emails. This is the result of some of my work from the past few years where I gave email coding trainings and I spent a lot of time helping other email developers on Slack, Twitter or forums.

Here are three of the (now) nine points long document.

Use the HTML5 doctype

The HTML5 doctype is clean, short and easy to remember. It’s used by a vast majority of email clients, so your code will inherit it anyway. Just be aware that some other email clients might use other doctypes and your email might end up being rendered in Quirks Mode. (See also: Which doctype should you use in HTML emails?)

<!-- Good example -->
<!DOCTYPE html>

Make it work without <style>

Not every email clients support <style> tags. <style> tags filtering can be:

“Making an email work” without <style> can mean a lot of different things. But I think first and foremost about:

  • Layout. An email without <style> should adjust to any width without horizontal scroll. I usually consider to go as low as 280px wide which reflects the width an email viewed on Gmail on an iPhone SE.
  • Branding. An email without <style> should reflect the branding of the sender.

Don’t split visuals

Avoid splitting an image into multiple files. This is important for several reasons:

  • Performance. Just like on the Web, The fewer HTTP requests the better. Downloading a single 50 Kb image is theoretically faster than downloading five 10 Kb images.
  • Accessibility. A single image will let you define a single clean alt text, and style it in case images aren’t visible.
  • WebKit adds small thin lines between images when using a CSS transform on a whole email. This is something used by numerous email clients to adjust the rendering of non responsive emails on smaller screens.
    The current beta of uses a CSS transform to adjust the display of an email within its preview pane. On Chrome or Safari, this can result in thin lines between split images like in this example.
  • Because shit happens. Email clients or user preferences may change how your email look. You don’t want this to happen:
    Image splitting gone wrong on a LinkedIn email. (Found under “She must be Canadian.” on Reddit.)

Want to learn more? Here are some of the topics addressed in the rest of the document:

  • The lang attribute
  • Semantic text markup
  • Tables for layout
  • Styles over attributes
  • Use margin or padding for spacing
  • Support Outlook at 120dpi

Head over to GitHub for the full Email Coding Guidelines document. It’s also available in french, and translations contribution are welcome!