unknown.rs.net.ua has no MX records.
Question and response
Question
dig unknown.rs.net.ua. MX
Answer
The response has no answer records.
Authority
rs.net.ua. 7200 SOA ns.rs.net.ua. mapmaster.rs.net.ua. 2026020401 7200 3600 1209600 7200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0