_spf.stampi.cz has no CNAME records.
Question and response
Question
dig _spf.stampi.cz. NS
Answer
The response has no answer records.
Authority
stampi.cz. 2277 SOA ns.forpsi.net. admin.forpsi.com. 2026021801 3600 1800 2592000 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0