mx.arakis.cz has no CNAME records.
Question and response
Question
dig mx.arakis.cz. NS
Answer
The response has no answer records.
Authority
arakis.cz. 2480 SOA ns.belleville.cz. admin.belleville.cz. 2026022003 10800 7200 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0