mx.oru.edu.gr has no CNAME records.
Question and response
Question
dig mx.oru.edu.gr. NS
Answer
The response has no answer records.
Authority
oru.edu.gr. 1741 SOA faye.ns.cloudflare.com. dns.cloudflare.com. 2397674482 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0