You may be mistaken from what the purpose of the ERG is intended.
"If I'm not mistaken, purpose of ERG for SOTI Surf is to relay all HTTP/HTTPS traffic from device to target destination and redirect it back."
The ERG is used to secure traffic between external devices and your internal web sites when using SOTI Surf.
In other cases (SOTI Hub & Exchange) ERG can be used to filter enrolled devices to access those resources (SOTI Hub/Repository & Exchange Server).
I do not believe it was intended as a filter for traffic for internal devices to communicate to internal sites or to monitor traffic from external devices to external sites.
Hope this helps!
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