Admin::NewslettersController
def create
    @news_letter = Newsletter.new(params[:newsletter])
    if @news_letter.save
      redirect_to admin_newsletters_path, notice: 'Рассылка успешно добавлена'
    else
      render action: 'new'
    end
  end

def delivery
    @news_letter.deliver
    redirect_to admin_newsletters_path
  end