Email open rates fell 12.8 percent on Black Friday and dropped 7.5 percent on Cyber Monday among consumers using Gmail, according to a new report from Sailthru. The other consumer email services including Yahoo, AOL and Hotmail saw an average 5.2 percent increase in open rates on Black Friday and a 17.5 hike on Cyber Monday. This report suggests that Gmail's "Promotions" tab could be hurting consumer engagement with email marketing.