mail.becloudby.com has no CNAME records.
Question and response
Question
dig mail.becloudby.com. NS
Answer
The response has no answer records.
Authority
becloudby.com. 600 SOA u1.hoster.by. support.hoster.by. 2025121203 43200 7200 604800 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0