I may be wrong here, but I believe the default queue lifetime for a message sitting in the qmail queue is 7 days. To me, that’s entirely too long to wait to deliver a defunct message considering most of them are probably SPAM bounces anyway.
Here is how to shorten the lifetime.
Change to the qmail control directory, assuming you use default locations on your server.
Set the timeout to the number of seconds you want the message to remain in the queue. This is done in the queuelifetime file. This file doesn’t normally exist by default. I’ll use 24 hours (86,400 seconds) as an example.
echo "86400" > queuelifetime
That’s it. Messages that don’t get delivered in 24 hours will be gone.