The ENS service consists of these individual services:
csnotifyd — The csnotifyd service sends notifications of events and todos (tasks). The csnotifyd service also subscribes to alarm events. When an alarm event occurs, csnotifyd sends an SMTP message reminder to each recipient.
enpd — The enpd service acts as the broker for event alarms. The enpd service receives notifications of alarms from the csadmind service, checks for subscriptions to this event, and then notifies the event’s subscribers by passing the subscribed-to alarm notifications to the subscriber. The default subscriber for the Calendar Server system is csnotifyd.
The enpd and csnotifyd services are not required to run on the same server as the cshttpd, csdwpd, or csadmind processes.