A recent evaluation conducted by Silverpop researchers of the e-mail practices of North America's largest online retailers revealed that some are engaging in risky strategies. In comparing e-mails sent during the same 30-day period in 2007 and 2008, the study found a sharp increase in e-mail frequency. Top retailers sent 23% more e-mails to subscribers last year than the year before. At the same time, only 28% offered subscribers choices at opt-in. This is down from 56% in 2007.