backmx.iol.cz has no CNAME records.
Question and response
Question
dig backmx.iol.cz. NS
Answer
The response has no answer records.
Authority
iol.cz. 10800 SOA dns.iol.cz. hostmaster.iol.cz. 2026021801 10800 3600 5184000 10800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0