The customer noticed that if they try to put a ticket "on hold" or "close" it, they don't get an email notification that it happened.
ServiceDesk 8.1 RU5
The following steps are provided as a reference of what to do in one of the possible scenarios that could apply to this situation. Deleting records out of the database without understanding the associations on that data and tables could cause leaving orphaned references.
161432 "Incident Management Timeouts and Escalations Fails to Process Messages Despite Being Configured Correctly"