Is it possible to use both Basic and NTLM Authentications on EWS?
I have read here https://msdn.microsoft.com/en-us/library/office/dn626019(v=exchg.150).aspx#sectionSection2
that it is not possible. Not that I am questioning msdn, but does not looks so, because I have option in exchange configuration to check both windows authentication and basic along each other. From that point it does not look that basic excludes NTLM.
You can at the IIS level configure it that way eg the defaults are all listed on https://technet.microsoft.com/en-us/library/gg247612(v=exchg.150).aspx. However the supported way which the documentation is outlining is that all configuration of virtual directories should be done via the Exchange Management tools (EMS etc). Autodiscover tells Outlook which authentication to use which is configurable via Set-WebServicesVirtualDirectory https://technet.microsoft.com/en-us/library/aa997233(v=exchg.160).aspx and this only allows you have one of the other which will then in turn configure the backend directories. So best practice is to choose one or the other.