mx-out.generalregistry.cz has no CNAME records.
Question and response
Question
dig mx-out.generalregistry.cz. NS
Answer
The response has no answer records.
Authority
generalregistry.cz. 3600 SOA ns.grdns.cz. admin.grdns.cz. 2026022401 3600 1800 2592000 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0