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)

Install the Premailer gem from RubyGems.

gem install premailer

or add it to your Gemfile and run bundle.

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

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)

1. nokogiri (default)
2. nokogiri_fast
3. 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

Premailer is tested on Ruby 2.1 and above. JRuby support is close; contributors are welcome. Checkout the latest build status on the Travis CI dashboard.

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

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'>

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

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.

Copyright by Alex Dunae (dunae.ca, e-mail 'code' at the same domain), 2007-2017. See LICENSE.md for license details.