find_preferred_part

# File railties/lib/rails/mailers_controller.rb, line 60
    def find_preferred_part(*formats)
      formats.each do |format|
        if part = @email.find_first_mime_type(format)
          return part
        end
      end

      if formats.any?{ |f| @email.mime_type == f }
        @email
      end
    end