Trying to replicate notification policies that we currently have for raw alarms, for raising incidents on Situations. When excludingunwanted alarms by 'message', I sometimes get a match and sometimes don't.
If the message field is of a situtaion, you could define the message based on the root cause or the most impacted alarm, ensuring that it aligns with the alarm.
This means that if it can use the situation name, which can be defined based on root cause or most impacted alarm, but unfortunately is currently very unpredictable if you base it on most impacted message (sometimes it is the message, sometimes it is the metric name, sometimes it is a combination of sections of previous messages). Ideally the name based on most impacted message would work correctly, but until that is resolved,Can work around this by excluding messages in the custom situation definition rather than the notification policy.