mx.wolfnet.cz has no CNAME records.
Question and response
Question
dig mx.wolfnet.cz. NS
Answer
The response has no answer records.
Authority
wolfnet.cz. 67 SOA ns1.wolfnet.cz. hostmaster.wolfnet.cz. 2026022115 600 300 604800 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0