mail18.rt.RU has no MX records.
Question and response
Question
dig mail18.rt.RU. MX
Answer
The response has no answer records.
Authority
rt.RU. 600 SOA ns1.rostelecom.RU. hostmaster.rt.RU. 2026022001 600 7200 1209600 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0