It is quite efficient for him: he spends a day reading email in “batch mode” every few months, and it saves him the cost of context-switching, and lets him focus on writing his books.
(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.
(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.