I can manage both work and mails. Whatever I do is no more than Alt-Tab away and while I'm waiting for the network and/or database to give me my data, I can fill in with other things. Besides, I start at 7.30 many mornings so there is a bit of slack time built into the day anyway. It depends on the company though. I worked for some stockbrokers in London and they were a pain in the butt. Company I'm with now are relatively relaxed. They expect the work to be done, but the cut some slack as well.
With the exception of internet extremes like downloading doubtful content, we are pretty well self-regulating, which is a nice place to be at. Noone here abuses the system. The rules are common sense and are often necessary for legal requirements, that sort of thing.