It can be anything! An apex, subdomain, or even a URL.
Results forwindows.microsoft.com.office.o365-proxy-prod.fenixprod.myshn.eu
www.windows.microsoft.com.office.o365-proxy-prod.fenixprod.myshn.eumicrosoft.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