mail.TATTELECOM.RU has no CNAME records.
Question and response
Question
dig mail.TATTELECOM.RU. NS
Answer
The response has no answer records.
Authority
tattelecom.ru. 1200 SOA ns.tattelecom.ru. root.tattelecom.ru. 2026022700 120 600 1814400 1200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0