google.com is your friend...
run /var/qmail/bin/qmail-qstat:
[root@host ]# /var/qmail/bin/qmail-qstat
messages in queue: 3
messages in queue but not yet preprocessed: 3
wget qmHandle:
wget http://kent.dl.sourceforge.net/sourceforge/qmhandle/qmhandle-1.2.0.tar.gz
read the --help option for more info, qmHandle comes with warnings...
if you delete the contents of the queues and don't have a backup, you won't be able to recover the deleted messages.
if you modify permissions or ownership of the queues you probably will break qmail.