mail.infoplus.com.pl has no CNAME records.
Question and response
Question
dig mail.infoplus.com.pl. NS
Answer
The response has no answer records.
Authority
infoplus.com.pl. 3289 SOA dns2.panelplus.pl. info.infoplus.com.pl. 2026013001 10800 3600 604800 10800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0