ns3.houfek.cz has no MX records.
Question and response
Question
dig ns3.houfek.cz. MX
Answer
The response has no answer records.
Authority
houfek.cz. 900 SOA ns1.houfek.cz. dnsadmin.houfek.cz. 121 900 600 86400 3600
Additional
. 0 OPT ; payload 4000, xrcode 0, version 0, flags 0