If you do it in EWS > Properties > General Setup > Extensible Services Setup > Proxy Server it may not unless you are using the Xerox App Gallery email app (Scan To Cloud Email)
If you set it via EWS > Properties > Connectivity > Setup > Proxy Server > Edit it should apply to anything that is not from the App Gallery or App Studio.
And yes, I realize email is not listed at the bottom of the next page, but the Xerox test LAN requires a Proxy so we can't email via Gmail/Office365/Godaddy etc until we enter the proxy on the device via this screen. It applies to NTP too and that isn't listed either.
then you can have the printer do a network trace when you attempt the scan, then save it and open it to see exactly what is happening on the LAN and exactly what servers/IP etc are being involved as well as what the responses are at each step.