How to stop automatic creation of /var/mail/$USER

[Sahil Tandon]

When I 'adduser' a new account, a /var/mail/$USER file is created.  This is
unnecessary as our MTA is configured to deliver mail directly to a user's
~/Maildir/, where the IMAP server looks by default.

There is nothing in the adduser or adduser.conf man pages that explains how
to manipulate (or, in my case, simply stop) the creation of this file.

--
Sahil Tandon <sahil at tandon.net>