smtp12.cez.cz has no MX records.
Question and response
Question
dig smtp12.cez.cz. MX
Answer
The response has no answer records.
Authority
cez.cz. 3600 SOA ns10.cez.cz. netmaster.cez.cz. 2026011502 14400 3600 604800 7200
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0