mail.itsweb.com.br has no CNAME records.
Question and response
Question
dig mail.itsweb.com.br. NS
Answer
The response has no answer records.
Authority
itsweb.com.br. 10719 SOA dns9.itsweb.com.br. redes.itsbrasil.net. 2026011502 10800 3600 1382400 10800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0