Direct Mail
"Today, direct mail has exploded—an explosion caused more than anything by computers. They make it possible to select names from mailing lists by every imaginable demographic classification, by frequency of purchase and by amount of purchase. With a computer you can remove duplicating between mailing lists and within a list—a process called 'merge and purge'. You can avoid mailing to people who don't like to receiving mailings." — David Ogilvy, Ogilvy on Advertising