The problem seems to be firewall related.. I can use the same version
of Evolution inside work (inside the LAN) and there I have no such
errors. But here at home, I have those errors.
You should use the external EWS URL when you are not on the internal
network. The servers can provide such addresses (one for internal and
one for external access point). When you run with debugging on (as
shown above) and in the EWS account Properties-> Receiving Email tab
click "Fetch URL", you'll see some XML data related to autodiscover.
That's what the server advertises. Search for Exchange.asmx there. It
can also depend whether you use NTLM or Basic authentication, I think.