Sorry from SAP Note: http://service.sap.com/sap/support/notes/1830360
2. Changes on the Java side (relevant from PI 7.11 onwards):
The alerting mechanism on the Java side has a technology for suppressing multiple alerts from PI 7.11 onwards, if many alerts are triggered by the same error source in a short period (for example, a fast-polling sender channel that keeps triggering the same error). This should help to reduce the system load and the number of similar alerts. This mechanism is always active and is not dependent on the above ABAP parameter or the "Suppress Multiple Alerts for This Rule" flag for the alert rule. Instead, the time interval is specified with AF Core Services parameter alerting.suppressInterval
Setting this parameter will make sure to say 5 minutes, will make sure that even if the poll interval is 60 seconds, instead of 5 alerts only 1 alert is triggered and so on. I havent tried this personally but that is my understanding. Let us know how this goes!