smtp.admin.grnet.gr has no CNAME records.
Question and response
Question
dig smtp.admin.grnet.gr. NS
Answer
The response has no answer records.
Authority
admin.grnet.gr. 10548 SOA ns0.admin.grnet.gr. administrator.admin.grnet.gr. 2019103015 28800 7200 604800 10800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0