A similarity exists between direct mail and e-mail in that the customers who spend more receive more touches — catalogs in the case of direct mail and promotional offers for e-mail. This "catalog effect" in e-mail, like direct mail, is in part driven by purchase behaviors: The more orders placed online, the more transactional messages and promotional offers follow. This causes more inbox competition, in much the same way as off-line efforts vie for attention in the physical mailboxes of top spenders.