http://www.qmail.org/qmailqueue-patch

QMAILQUEUE (http://www.qmail.org/qmailqueue-patch) patch to check for a
QMAILQUEUE environment variable for a replacement program to qmail-queue. This
allows virus scanners or other programs to perform some action before rejecting
the email or putting it into the queue with the real qmail-queue prorgram.
simscan and qmail-scanner both use this method. By Bruce Guenter.