spf.nethost.cz has no CNAME records.
Question and response
Question
dig spf.nethost.cz. NS
Answer
The response has no answer records.
Authority
nethost.cz. 864 SOA dns.nethost.cz. hostmaster.nethost.cz. 2026030501 14400 36000 3600000 864
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0