ruby script/plugin install git://github.com/purify/mail_style.git

Simply add the css method to your deliver actions:

class Notifier < ActionMailer::Base
  def welcome_email
    css :email
    
    subject 'Welcome Aboard'
    recipients 'someone@example.com'
    from 'jimneath@googlemail.com'
    sent_on Time.now
  end
end

This will look for a css file called email.css in your public/stylesheets folder. The css method can take either a string or a symbol. You can also pass the css file name with or without the .css extension.

There is currently no advanced documentation for this plugin.