We have enabled EDM.HighlightAllMatchesInProximity by adjusting the values in ServerAdvancedSettingsWhitelist.properties, but when we test this functionality in our email prevent server it does not work.
Release : 15.7
This functionality was never designed to work on cloud servers which is why the setting is not available by default in the server's advanced settings.
This functionality can be manually added to a cloud server via an escalation ticket to cloud ops.
If you modify ServerAdvancedSettingsWhitelist.properties those settings do not automatically carry to cloud servers as there is no API to control the functionality for them.
Modifying this setting only enables it to show in the UI, but the value is not actually received by the cloud server.
Therefore this functionality must be manually turned on or off via cloud ops.