The agent registration feature requires a client computer to be allowed to communicate with Notification Server before it can be managed by this Notification Server. The default agent registration policy allows all computers to communicate with Notification Server. However, you can create custom agent registration policies that allow or block certain computers.
After the agent registration policy allows or blocks a computer, you can only change its status manually on the Agent Registration Status report page. For example, you can allow or block the computers that are in the pending state. You can also revoke the registration of the agents that you have previously allowed.