It can be anything! An apex, subdomain, or even a URL.
Results forres.office365.com.4test12.o365---bdl.btfrancedemo.myshn.net
www.res.office365.com.4test12.o365---bdl.btfrancedemo.myshn.netoffice365.com.4test12.o365---bdl.btfrancedemo.myshn.netcom.4test12.o365---bdl.btfrancedemo.myshn.net4test12.o365---bdl.btfrancedemo.myshn.neto365---bdl.btfrancedemo.myshn.netbtfrancedemo.myshn.netmyshn.netnet