From a bug report, reading a scroll
of mail violates illiterate conduct and he requests that it not do so.
I didn't go that far, since unlike needing to read the Book of the Dead
to be able to finish the game, reading scrolls of mail is completely
voluntary and someone attempting voluntary challanges can choose not to
do it. Instead, this issues a prompt to require confirmation if reading
such a scroll will be the first violation of that conduct. Ordinary
players can answer no and then use '!' to read mail from a shell. I'm not
sure what'll happen to players on public servers who aren't given access
to a shell. Usually they wouldn't be able to get mail either, so more
elaborate servers like the one at nethack.alt.org which allow players to
use mail to communicate with each other will have to come up with their
own solution (perhaps by providing a mail-reader-only shell).