The VCS engine, HAD, stores messages to be sent to notifier. After every 180 seconds, HAD tries to send all the pending notifications to notifier. When HAD receives an acknowledgement from notifier that a message is delivered to at least one of the recipients, it deletes the message from its queue. For example, if two SNMP consoles and two email recipients are designated, notifier sends an acknowledgement to HAD even if the message reached only one of the four recipients. If HAD does not get acknowledgement for some messages, it keeps on sending these notifications to notifier after every 180 seconds till it gets an acknowledgement of delivery from notifier. An error message is printed to the log file when a delivery error occurs.