mail.flexline.ru has no CNAME records.
Question and response
Question
dig mail.flexline.ru. NS
Answer
The response has no answer records.
Authority
flexline.ru. 3063 SOA ns4.flexline.ru. root.flexline.ru. 2025092501 10800 7200 86400 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0