Из nethack Guidebook: > A mail daemon may run up and deliver mail to you as a scroll of mail (on versions compiled with this feature). To use this feature on versions where NetHack mail delivery is triggered by electronic mail appearing in your system mailbox, you must let NetHack know where to look for new mail by setting the ``MAIL'' environment variable to the file name of your mailbox. You may also want to set the ``MAILREADER'' environment variable to the file name of your favorite reader, so NetHack can shell to it when you read the scroll. On versions of NetHack where mail is randomly generated internal to the game, these environment variables are ignored. You can disable the mail daemon by turning off the mail option.