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 gem is a 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

gem install premailer

Example

require 'premailer'

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

# Write the plain-text output (must come before to_inline_css)
File.write "output.txt", premailer.to_plain_text

# Write the HTML output
File.write "output.html", premailer.to_inline_css

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

Adapters

nokogiri (default)
nokogiri_fast (20x speed, more memory)
nokogumbo

(hpricot adapter removed, use ~>1.9.0 version if you need it)

Picking an 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'>

Plain text version

Premailer can generate a plain text version of your HTML. Links and images will be inlined.

For example

<a href="https://example.com" >
  <img src="https://github.com/premailer.png" alt="Premailer Logo" />
</a>

will become

Premailer Logo ( https://example.com )

To ignore/omit a section of HTML content from the plain text version, wrap it with the following comments.

<!-- start text/html -->
<p>This will be omitted from the plain text version.</p>
<p>
  This is extremely helpful for <strong>removing email headers and footers</strong>
  that aren't needed in the text version.
</p>
<!-- end text/html -->

Configuration options

For example:

Premailer.new(
  html, # html as string
  with_html_string: true,
  drop_unmergeable_css_rules: true
)

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.

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.