It can be anything! An apex, subdomain, or even a URL.
Results forwww.activedirectory.windowsazure.com.office.o365-proxy-prod.fenixprod.myshn.eu
activedirectory.windowsazure.com.office.o365-proxy-prod.fenixprod.myshn.euwindowsazure.com.office.o365-proxy-prod.fenixprod.myshn.eucom.office.o365-proxy-prod.fenixprod.myshn.euoffice.o365-proxy-prod.fenixprod.myshn.euo365-proxy-prod.fenixprod.myshn.eufenixprod.myshn.eumyshn.eueu