Conventional wisdom has long held that your mailing list is one of the most critical components of a successful direct mail campaign. Guess what? It’s still true. After all, if you’re selling pet supplies you’re not going to have much success if you mail your cards, letters, or catalogs to people that don’t own pets. A huge part of direct mail success is getting the right message to the right people. So how do you select the right list? Here are four keys.