ext.robobackend2.mail.corp.hostcomm.ru has no CNAME records.
Question and response
Question
dig ext.robobackend2.mail.corp.hostcomm.ru. NS
Answer
The response has no answer records.
Authority
corp.hostcomm.ru. 600 SOA pdns.infra.nic.ru. noc-dns.nic.ru. 2022021002 14400 3600 2592000 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0