At work we has one or two cases where it would be useful to send mails to /dev/null.
Looking in google for a solution lead to the following solution (presented in
http://stackoverflow.com/questions/120587/what-is-the-best-way-to-forward-a-single-qmail-alias-to-dev-null)
either create an alias with only a comment and no delivery instructions:
$> echo "# drop all messages on the floor" > ~alias/.qmail-devnull(note the # indicating a comment) or with
$> echo -e '|cat >/dev/null' "\n" > ~alias/.qmail-devnullnote however that the first seems nicer to me.