osmtp6.mail.hol.gr has no CNAME records.
Question and response
Question
dig osmtp6.mail.hol.gr. NS
Answer
The response has no answer records.
Authority
hol.gr. 7200 SOA ns0.hol.gr. hostmaster.hol.gr. 202511000 28800 7200 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0