A message is removed from the delivery queue without generating a Non-Delivery Report (NDR) on SMG.
554 5.7.0 manually failed
This behavior is expected, and the SMG is working by its design.
Please note, that when a message is manually deleted from the delivery queue, either from the Command Line Interface (CLI) or from the Control Center, the message is removed from the queue and a Non-Delivery Report (NDR) is NOT generated.