_spf.usp.br has no CNAME records.
Question and response
Question
dig _spf.usp.br. NS
Answer
The response has no answer records.
Authority
usp.br. 151 SOA a.dns.usp.br. hostmaster.usp.br. 2018079091 14400 3600 1209600 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0