Want a sure-fire way to get your customers to open your direct-mail piece? Try this technique that nobody can resist: Customers will always open an envelope with a lump in it or a small box of anything. Put a swatch or sample of a new product you want to promote inside an envelope. Obviously, some products just can't be squeezed in, but don't worry. Just include something that relates to your product or something that you can play off of in a product announcement. For instance, a note saying "If you want to test the new phone system, just whistle" could accompany a bright, shiny whistle.