mail29.world4you.com has no CNAME records.
Question and response
Question
dig mail29.world4you.com. NS
Answer
The response has no answer records.
Authority
world4you.com. 175 SOA ns-ionos.ui-dns.com. dnsadmin.ionos.com. 2025042089 10800 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0