I thought it was pretty interesting that he no longer uses email. He did use it from (1975 - 1990), and he still works at Stanford.
https://www-cs-faculty.stanford.edu/~knuth/news.html
"2018 began for me with an absolutely incredible 80th birthday celebration called Knuth80, held in the delightful city of Piteå in northern Sweden. ..."
So maybe he's just using that email-via-printouts thing as a ruse to avoid having to answer to emails from "important people" expediently? I would totally pull that move if I could.
> My secretary also prints out all nonspam email messages addressed to taocp@cs.stanford.edu or knuth-bug@cs.stanford.edu, so that I can reply with written comments when I have a chance
(Note that the only email he reads is bug reports: if you send something by email that is not a bug report, he says he ignores it, though I've been able to sneak in an odd thing or two (a comment on a TAOCP section) by including it along with bug reports… the catch of course is that to use this trick, you have to find an actual bug in the books.)
The emails are printed for him by his secretary on the back of one-sided printouts, so he's not wasting any “new” paper for the emails. He scrawls (with pencil) his replies on the printouts, and hands off the pile of outgoing mail to his secretary (who only comes in once a week or something), who contacts the recipients, asks them for their postal mail address, and sends his reply by post.
It works very well for him, and he doesn't have to waste time filtering email, typing into a computer, etc. He does everything with pen-and-paper (including writing programs like TeX and METAFONT over several months, without typing them up into a computer until the very end), so it just matches his most comfortable working environment.
I mean, that's a drop compared to the paper waste in most companies. And it's not inefficient. Paper copies make annotations easier which makes replying easier and better quality.
Also, this is unlikely to be more than a trickle. He talks about spending a day every three months responding to correspondence, as well as rather making a point out of refusing to respond to unsolicited emails. Chances are that his secretary also simply deals with a good deal of the email in the way, you know, a secretary does.
Eventually they decided to get more modern, and his secretary would scan in the response and send it as an e-mail attachment.