b.nic.rs has no MX records.
Question and response
Question
dig b.nic.rs. MX
Answer
The response has no answer records.
Authority
nic.rs. 900 SOA a.nic.rs. hostmaster.nic.rs. 2026021290 14400 3600 604800 900
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0