ActionMailer Inline CSS

Seamlessly integrate Alex Dunae's premailer gem with ActionMailer.

Problem?

The Guide to CSS support in email from campaignmonitor.com shows that Gmail doesn't support <style> tags.

Thus, the only correct way to send HTML emails is when CSS is inlined on each element.

Email Client Popularity:

Outlook 27.62%
iOS Devices 16.01%
Hotmail 12.14%
Apple Mail 11.13%
Yahoo! Mail 9.54%
Gmail 7.02%

Gmail may only make up 7% of all email clients, but it's a percentage you can't ignore!

Solution

Inlining CSS is a pain to do by hand, and that's where the premailer gem comes in.

From http://premailer.dialect.ca/:

  • CSS styles are converted to inline style attributes. Checks style and link[rel=stylesheet] tags and preserves existing inline attributes.
  • Relative paths are converted to absolute paths. Checks links in href, src and CSS url('')

The actionmailer_inline_css gem is a tiny integration between ActionMailer and premailer.

Inspiration comes from @fphilipe's premailer-rails3 gem, but I wasn't completely happy with it's conventions.

Installation & Usage

To use this in your Rails app, simply add gem "actionmailer_inline_css" to your Gemfile.

  • If you already have an HTML email template, all CSS will be automatically inlined.
  • If you don't include a text email template, premailer will generate one from the HTML part. (Having said that, it is recommended that you write your text templates by hand.)

Additional Helpers

Rails does not provide any helpers for adding 'embedded' CSS to your layouts (and rightly so!), but the following helper is now available for your mail layouts:

embedded_style_tag(file = mailer.mailer_name)

  • Embeds CSS loaded from a file, in a style tag.
  • File can be given with or without .css extension
  • Default path for mailer css files is public/stylesheets/mailers/#{mailer_name}.css

Example

Given a mailer called BuildMailer, you can add the following line to the <head> section of app/views/layouts/build_mailer.html.erb:

<%= embedded_style_tag %>

This will embed the CSS found at public/stylesheets/mailers/build_mailer.css.


If you wanted to include different CSS for each mail template, you could do something like this:

<% content_for 'head' do %>
  <%= embedded_style_tag 'error_notification' %>
<% end %>

Other Notes

It may seem like a waste of resources to generate HTML, then parse it with Nokogiri, alter it, and finally re-render it. However, there is simply no other way to do it. ERB templates contain HTML tags in plain text, so the output must be parsed. On-the-fly CSS inlining could theoretically be built for Haml templates, but it would be far too much effort for such a small use-case.