mail.ntelecom.com.br has no CNAME records.
Question and response
Question
dig mail.ntelecom.com.br. NS
Answer
The response has no answer records.
Authority
ntelecom.com.br. 537 SOA srv1.ntelecom.com.br. postmaster.ntelecom.com.br. 2024041600 3600 900 1209600 43200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0