postman.dragon.cz has no CNAME records.
Question and response
Question
dig postman.dragon.cz. NS
Answer
The response has no answer records.
Authority
dragon.cz. 2950 SOA ns.dragon.cz. hostmaster.dragon.cz. 2026030200 7200 3600 1209600 14400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0