Everybody has his limit in handling emails. For one 10 per day are too much, another handles 150 without any problems. But sooner or later, everybody of us have to declare: it’s too much.
I have had a time in my life in which I have had to handle 750 mails per day in average. Nobody can say that this is possible to do. But that was the time I started a very strict and consequent filtering and categorization. However it still was too much. The combination of importance and urgency was back-breaking.