E-mails which are sent in about the various books used to be printed out and responded to --- I got a $2.88 physical reward check for finding an error and a point of improvement in _Digital Typography_. Not sure how they are handled now. Trying to find an error or point of improvement in v4f7 so that I can get an account at:

https://www-cs-faculty.stanford.edu/~knuth/boss.html

(usually, I do find errors in books, esp. e-books, which reminds me, I need to pick up the corrected 3rd printing of _The Fall of Arthur_ by J.R.R. Tolkien before I read it again, since that should have the error I found corrected).

Inboxes don’t have to be digital. Inboxes, digital or physical, can be handled by other people.

In any case, someone beyond the publisher will still get inundated with corrections about the PDFs and likely will demand their reward for it.

"Inbox" used to be literally the box/tray on your desk where people would leave work for you in written letters. That's where email got the term.

Amusingly in my first job in the 90s they still assigned each desk a labeled inbox and an outbox (two trays on the desk), but by then it was all email already so nobody ever used those on my desk. But they sat there for a few years as a memento to the 80s!