_dmarc.sfnet.com.br has no CNAME records.
Question and response
Question
dig _dmarc.sfnet.com.br. NS
Answer
The response has no answer records.
Authority
sfnet.com.br. 1945 SOA master.frionline.com.br. adtech.frionline.com.br. 2026022000 3600 600 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0