mail18.RT.RU has no CNAME records.
Question and response
Question
dig mail18.RT.RU. NS
Answer
The response has no answer records.
Authority
rt.RU. 149 SOA ns1.rostelecom.RU. hostmaster.rt.RU. 2026022502 600 7200 1209600 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0