Mystery resolved.
The actual link to use is
https://pod51046.outlook.com/ews/services.wsdl
instead of
https://pod51046.outlook.com/ews/exchange.wsdl (which Oleg's blog actually mentioned, and I overlooked).
The generic
https://outlook.office365.com/ews/services.wsdl also works; I think that after having read somewhere that the actual URL is a pod... one, I doggedly kept trying that one after resolving it.
Also, SOAP UI asks me 2 times 3 = 6 times for the login credentials when setting up the test project. I just was not persistent enough.
The *EWS endpoint* is
https://pod51046.outlook.com/ews/exchange.asmx
