mail.sitel.com.br has no CNAME records.
Question and response
Question
dig mail.sitel.com.br. NS
Answer
The response has no answer records.
Authority
sitel.com.br. 6102 SOA ns1.sitel.com.br. noc.clicknet.net.br. 2024120401 3600 120 1209600 10800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0