Use Dead-Letter Queue (USEDLQ)

This attribute determines whether the dead-letter queue (or undelivered message queue) is used when messages cannot be delivered by channels.

Possible values are:

NO: Messages that cannot be delivered by a channel are treated as a failure. The channel either discards these messages, or the channel ends, in accordance with the setting of NPMSPEED.
YES (default): If the queue manager DEADQ attribute provides the name of a dead-letter queue, then it is used, otherwise the behavior is as for NO.