Schaumburg, Ill.—Email volume in the second quarter rose by 17.9% compared with the same period last year, with open rates up 7.2% year-over-year, according to a report from Experian Marketing Services. According to Experian's “Quarterly Email Benchmark Study,” a rolling analysis of 5 million unique email opens in the past 12 months, second-quarter click rates remained virtually steady compared with the year-earlier period, at 2.3%. Revenue per email—a calculation of the average amount earned for each delivered email—was 11 cents, compared with 12 cents in the year-earlier period. Fifty percent of unique email opens occurred on a mobile device during the second quarter, Experian said. Apple Inc.'s iPhone accounted for 68% of those, followed by Apple's iPad at 16%, and mobile devices powered by the Android operating system at 13%. Apple also dominated mobile transactions with iPhones and iPads accounting for 88% of all mobile-conducted deals.