That's ludicrous and unbelievable. Either the standard deviation is small, which implies that almost everybody does that, or the standard deviation is large, which implies there's a significant percentage of people spending more than 8 hours a day checking email. Either way I suspect this is more a demonstration of the unreliability of self-reporting than an accurate reflection of reality. Either that, or there's a significant deviation between what is being reported and what the wording of the question was on the survey. (I can imagine spending hours a day doing a task you received over email, but if your boss asks you for a report of something or other over email and you spend three hours assembling it, that could be "three hours related to email" but not "three hours checking email".)