Email is a wonderful thing for people whose role in life is to be on top of things. But not for me; my role is to be on the bottom of things. What I do takes long hours of studying and uninterruptible concentration. – Donald Knuth
One of the most influential computer scientists stopped using email in 1990. He accepts letters, prints them out, and replies with written comments.
Dijsktra, another famous computer scientist, only used email for a few years. It's not just computer scientists without an email but even prolific writers like Umberto Eco.
I don't even have an e-mail address. I have reached an age where my main purpose is not to receive messages.' -- Umberto Eco, quoted in the New Yorker
Or the pianist Glenn Gould, who refused to play or practice without a specific piano chair – an uncomfortable-looking and unusually low wooden chair from his childhood. After twenty years, he was still using it. By then, it was only a bare frame.
Sometimes the obvious optimizations drive us towards local maximums, not global ones. Would Knuth be more productive if he was a savvy email user? Would he have published more if he didn't spend so much time writing the TeX and METAFONT typesetting languages?
Hard to tell. Maybe he was able to find a focus without the distractions of neverending correspondence. Maybe Gould's chair brought him comfort in other ways.