smart-mailer.rb

# Automatically generates the plain-text version of emails from the html 
# template using premailer.

class SmartMailer < ActionMailer::Base

  protected

  def collect_responses(headers)
    responses = super(headers)

    if responses.none? { |r| r[:content_type] == 'text/plain' }
      html = responses.find { |r| r[:content_type] == 'text/html' }
      if html
        premail = Premailer.new(html[:body], with_html_string: true)
        responses << { content_type: 'text/plain', body: premail.to_plain_text }
      end
    end

    responses
  end
end