Depends where you set the Proxy.
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.
If your firmware is up to date and you know how to use Wireshark,
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.
EWS > Properties > Security > Logs > Network Troubleshooting
