One needs to find the option “Delete clients that have not connected for X days” within the Symantec Endpoint Protection Manager (SEPM) settings.
Note: Clients that have been imported from Active Directory cannot be deleted using the below steps. Clients imported from Active Directory to the SEPM need to be deleted from Active Directory and then synced with SEPM in order for the clients to be removed. It will take approximately 45 days for the decommissioned clients to drop out all of the reports.