smtp10.redlink.pl has no CNAME records.
Question and response
Question
dig smtp10.redlink.pl. NS
Answer
The response has no answer records.
Authority
redlink.pl. 220 SOA carlos.ns.cloudflare.com. dns.cloudflare.com. 2397651029 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0