mail.rambler.com.pl has no CNAME records.
Question and response
Question
dig mail.rambler.com.pl. NS
Answer
The response has no answer records.
Authority
rambler.com.pl. 5515 SOA rambler.com.pl. rg.rambler.com.pl. 2025040901 28800 7200 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0