cdnsa.nic.RU has no MX records.
Question and response
Question
dig cdnsa.nic.RU. MX
Answer
The response has no answer records.
Authority
nic.RU. 300 SOA ns5.nic.RU. noc-dns.nic.RU. 650335418 14400 3600 2592000 600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0