Apex domains cannot have CNAME records.
Question and response
Question
dig admin.uoc.gr. NS
Answer
admin.uoc.gr. 5 NS ns.uoc.gr.
admin.uoc.gr. 5 NS honos.admin.uoc.gr.
Authority
The response has no authority records.
Additional
ns.uoc.gr. 5 A 147.52.80.1
honos.admin.uoc.gr. 5 A 147.52.104.11
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0