The Alerter subkey stores configuration data for the Alerter service. This service sends messages to users warning them of impending resource, security, or access problems on the server. The messages appear in a message box on the user's display. Typically, the Alerter service alerts users when a printer is running out of paper or the disk on a file server is nearly full.
To specify users who receive messages about the server, use the Send Administrative Alerts to preference (Computer Configuration\Windows Settings\Administrative Templates\Administrative Services) in Group Policy.