Firstly, as Bastiaan says, the queue must be configured to enable retries (ie Max Attempts > 1). After that, it's all down to how you use the inputs to the Mark Exception stage. You can choose not to retry (because there may be no point) or whether to take possession of the new retry item immediately rather than use Get Next Item. A retry item is effectively a clone of the original item, so you will see the number of item in your queue increase with each retry.
