SIGNL4 can filter incoming events (received by email, webhook or REST API). This is handled through a keyword whitelist filter. The keyword whitelist is comprised from all keywords of all signl categories.
Here is an article describing how the whitelist is enabled and how it works: https://www.signl4.com/blog/april-2019-update-event-filtering/
Received events which get filtered out and do not raise an alert notification flow, are still visible in the event journal (accessible through https://account.signl4.com/manage/Signls ).
They are marked with a "Filtered" status.