mailserver.ampernet.com.br has no CNAME records.
Question and response
Question
dig mailserver.ampernet.com.br. NS
Answer
The response has no answer records.
Authority
ampernet.com.br. 3317 SOA ns1.ampernet.com.br. postmaster.ampernet.com.br. 2025102805 3600 3600 86400 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0