mx2.orion.rs has no CNAME records.
Question and response
Question
dig mx2.orion.rs. NS
Answer
The response has no answer records.
Authority
orion.rs. 265 SOA auth1.oriontelekom.com. admin.oriontelekom.rs. 2026021901 7200 1800 1209600 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0