From Time, April 9, 2012 (p. 42):

Corporate email storage is growing 20% to 25% a year, thanks in part to heavier file sharing, according to data consultancy Osterman Research. The data dump sucks $997 billion in productivity out of US workers annually, according to research firm Basex. ‘Email is an inherently poor tool for accessing information,’ says Forrester Research analyst T J Keitt. Much of the drag is due to bad habits: an estimated 30% of email is ‘occupational spam’ caused by overuse of CC, BCC and REPLY ALL.