_spf.ketnet.cz has no MX records.
Question and response
Question
dig _spf.ketnet.cz. MX
Answer
The response has no answer records.
Authority
ketnet.cz. 3600 SOA ns.servery.cz. hostmaster.active24.cz. 2026021801 10800 1800 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0