mx1.rtcomm.RU has no CNAME records.
Question and response
Question
dig mx1.rtcomm.RU. NS
Answer
The response has no answer records.
Authority
rtcomm.ru. 5556 SOA ns01.rtcomm.ru. noc.rtcomm.ru. 2026012903 18000 3600 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0