Hopkins took inspiration from the success of two former peddlers, Aaron Montgomery Ward and Richard Sears, whose mail-order catalogues (Montgomery Ward's and Sears's) built a thriving business on the back of a federally subsidized carrier. Thus did the U.S. Post Office first become a platform for commercial harvesting of attention. Hopkins began to post more than 400,000 pamphlets for Dr. Shoop's every day, reaching millions with this pioneering effort at "direct mail" advertising, or what we now call "spam."

Tim Wu, The Attention Merchants, loc. 99