Email marketing messages led to 23.9 percent of transactions on Cyber Monday, according to a new report from research firm Custora. The company looked at the transactions of 100 online retailers, whose traffic includes 100 million shoppers, to explore the influence of email on orders. Interestingly, email was less effective this year than last year. According to the metrics, 27.7 percent of orders on Cyber Monday last year were led by email.