@return the number of unsuccessful previous attempts to deliver this message. If this value is non-zero it can be
taken as an indication that the delivery might be a duplicate. On first delivery, the value is zero. It is
incremented upon an outcome being settled at the sender, according to rules defined for each outcome.
@see <a href="http://docs.oasis-open.org/amqp/core/v1.0/os/amqp-core-messaging-v1.0-os.html#type-header">AMQP specification</a>
@return the number of unsuccessful previous attempts to deliver this message. If this value is non-zero it can be taken as an indication that the delivery might be a duplicate. On first delivery, the value is zero. It is incremented upon an outcome being settled at the sender, according to rules defined for each outcome. @see <a href="http://docs.oasis-open.org/amqp/core/v1.0/os/amqp-core-messaging-v1.0-os.html#type-header">AMQP specification</a>