smtp3.uth.gr has no CNAME records.
Question and response
Question
dig smtp3.uth.gr. NS
Answer
The response has no answer records.
Authority
uth.gr. 3600 SOA ns1.uth.gr. root.ns1.uth.gr. 2026022700 14400 3600 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0