This is an upstream bug, but it makes debian package to fail in some circumstances. /usr/share/doc/mailfront/backend-qmail.html states that qmail-queue location is expected where, first, $QMAILQUEUE says, or, second, as $QMAILHOME/bin/qmail-queue names, while previously say that $QMAILHOME defaults to /var/qmail. This is broken whithin the code: function data_start(), within backend-qmail, resolves qmail-queue location _before_ resolving $QMAILHOME, so the 'second' assumption above turns mistaken.