mx.it-service.io has no CNAME records.
Question and response
Question
dig mx.it-service.io. NS
Answer
The response has no answer records.
Authority
it-service.io. 8788 SOA ns.gblnet.ru. vvv.gblnet.ru. 2026021902 3600 1200 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0