How can I prevent Postfix to send messages waiting in the incoming / active queue for more than 1 day?

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http://serverfault.com – I have a first line / graveyard postfix servers structure, the first line servers send messages to the graveyard when it received a soft fail. But sometimes I guess the queues are too busy and messages are locked in the incoming queue and cannot be sent but days after. I prefer to discard mails than sending very old ones. Setting the maximal_queue_lifetime won't work because it needs to send the message at least once, and if the message is too old, I don't want it be be sent not even once. (HowTos)