mx5.ipartners.pl has no CNAME records.
Question and response
Question
dig mx5.ipartners.pl. NS
Answer
The response has no answer records.
Authority
ipartners.pl. 10800 SOA ns1.ikp.pl. hostmaster.ikp.pl. 2026021900 10800 3600 3600000 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0