mx2.rt-rk.com has no CNAME records.
Question and response
Question
dig mx2.rt-rk.com. NS
Answer
The response has no answer records.
Authority
rt-rk.com. 10695 SOA dns1.orion.rs. admin-cpanel32.sezamhosting.com. 2025121600 3600 1800 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0