5.2.5. Durable Message State After Restart

When a durable queue is re-established after a restart of the broker, any messages that were marked as persistent and were not reliably delivered before the broker shut down are recovered. The broker does not have information about the delivery status of these messages. They may have been delivered but not acknowledged before the shutdown occurred. To warn receivers that these messages have potentially been previously delivered, the broker sets the redelivered flag on all recovered persistent messages.

Consuming applications should treat the redelivered flag as a suggestion.