(You might wanna remove the <> they screw up the link.)

Email seems to be an analogy for communication or perceiving information, or at least a predecessor of more fast-paced forms of that.

Could it be these new forms are so efficient and fast-paced, they overload our brain? Before the TV (which had limitations at start as well), there was telephone and radio. Both were limited. Telephone was expensive (monopoly yada yada), and radio informative (before the ~60s).

What Knuth did is enforce snail mail. This creates an artificial barrier, increasing signal to noise ratio.

"Bad roads act as filters... bad roads bring good people, good roads bring bad people"

-- Joseph Wood Krutch

as evanlivingston mentioned above, Knuth is in the position to cut off people from his email; trying to run a digital company without an email is kind of like trying to be a lumberjack without an axe