mxfront01.RT-DC.ru has no CNAME records.
Question and response
Question
dig mxfront01.RT-DC.ru. NS
Answer
The response has no answer records.
Authority
RT-DC.ru. 210 SOA ns1.ngenix-dns.net. noc.ngenix.net. 1 7200 600 1209600 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0