If you have created notification groups and then configured individual rules to send their notification to one or more groups then the notification works as follows:
Notification of an event takes place when a rule is executed
and the severity level for a given rule changes. For example,
if during execution of a rule, the result of the rule goes
from severity level
Critical, the configured notification
groups will get one email with the detail of the event and
If the status of the event has not changed when the rule is next executed, no new email is sent.
This is true whether the rule is executed as part of it's normal schedule or execution of the rule has been explicitly requested.
SNMP notifications are sent each time a given rule is executed, irrespective of the current or returned state.