smtp.mm.pl has no CNAME records.
Question and response
Question
dig smtp.mm.pl. NS
Answer
The response has no answer records.
Authority
mm.pl. 10800 SOA ns.multimedia.pl. ns.multimedia.pl. 2025052603 3600 900 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0