mailer.it-service.io has no MX records.
Question and response
Question
dig mailer.it-service.io. MX
Answer
The response has no answer records.
Authority
it-service.io. 86400 SOA ns.gblnet.ru. vvv.gblnet.ru. 2026022502 3600 1200 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0