Premailer README

What is this?

For the best HTML e-mail delivery results, CSS should be inline. This is a huge pain and a simple newsletter becomes un-managable very quickly. This script is my solution.

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('')
CSS properties are checked against e-mail client capabilities
- Based on the Email Standards Project's guides
A plain text version is created (optional)

Installation

Install the Premailer gem from RubyGems.

gem install premailer

or add it to your Gemfile and run bundle.

Example

require 'premailer'

premailer = Premailer.new('http://example.com/myfile.html', :warn_level => Premailer::Warnings::SAFE)

# Write the plain-text output
# This must come before to_inline_css (https://github.com/premailer/premailer/issues/201)
File.open("output.txt", "w") do |fout|
  fout.puts premailer.to_plain_text
end

# Write the HTML output
File.open("output.html", "w") do |fout|
  fout.puts premailer.to_inline_css
end

# Output any CSS warnings
premailer.warnings.each do |w|
  puts "#{w[:message]} (#{w[:level]}) may not render properly in #{w[:clients]}"
end

Adapters

Premailer's default adapter is nokogiri if both nokogiri and nokogumbo are included in the Gemfile list. However, if you want to use a different adapter, you can choose to.

There are three adapters in total (as of premailer 1.10.0)

nokogiri (default)
nokogiri_fast
nokogumbo

hpricot adapter removed due to its EOL, please use ~>1.9.0 version if You still need it..

NokogiriFast adapter improves the Algorithmic complexity of the running time by 20x with a slight compensation on memory. To switch to any of these adapters, add the following line. For example, if you want to include the NokogiriFast adapter,

Premailer::Adapter.use = :nokogiri_fast

Ruby Compatibility

See .github/workflows/actions.yml for which ruby versions are tested. JRuby support is close, contributors are welcome.

Premailer-specific CSS

Premailer looks for a few CSS attributes that make working with tables a bit easier.

CSS Attribute	Availability
-premailer-width	Available on `table`, `th` and `td` elements
-premailer-height	Available on `table`, `tr`, `th` and `td` elements
-premailer-cellpadding	Available on `table` elements
-premailer-cellspacing	Available on `table` elements
-premailer-align	Available on `table` elements
data-premailer="ignore"	Available on `link` and `style` elements. Premailer will ignore these elements entirely.

Each of these CSS declarations will be copied to appropriate element's attribute.

For example

table { -premailer-cellspacing: 5; -premailer-width: 500; }

will result in

<table cellspacing='5' width='500'>

Configuration options

The behavior of Premailer can be configured by passing options in the initializer.

For example, the following will accept HTML from a string and will exclude unmergeable css from being added to the <head> of the output document.

premailer = Premailer.new(html_string, with_html_string: true, drop_unmergeable_css_rules: true)

See here for a full list of the available options.

Contributions

Contributions are most welcome. Premailer was rotting away in a private SVN repository for too long and could use some TLC. Fork and patch to your heart's content. Please don't increment the version numbers, though.

A few areas that are particularly in need of love:

Improved test coverage
Move un-repeated background images defined in CSS for Outlook

Credits and code

Thanks to all the wonderful contributors for their updates.

Thanks to Greenhood + Company for sponsoring some of the 1.5.6 updates, and to Campaign Monitor for supporting the web interface.

The source code can be found on GitHub.

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