mail.partner.infoplus.com.pl has no CNAME records.
Question and response
Question
dig mail.partner.infoplus.com.pl. NS
Answer
The response has no answer records.
Authority
partner.infoplus.com.pl. 10384 SOA dns1.panelplus.pl. info.infoplus.com.pl. 2026030403 10800 3600 1209600 10800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0