class ActionMailer::InlinePreviewInterceptor

def transform! # :nodoc:
  return message if html_part.blank?
  html_part.body = html_part.decoded.gsub(PATTERN) do |match|
    if part = find_part(match[9..-2])
      %[src="#{data_url(part)}"]
    else
      match
    end
  end
  message
end