_spf.rdstation.com.brinclude:sendgrid.net has no CNAME records.
Question and response
Question
dig _spf.rdstation.com.brinclude:sendgrid.net. NS
Answer
The response has no answer records.
Authority
net. 780 SOA a.gtld-servers.net. nstld.verisign-grs.com. 1772280766 1800 900 604800 900
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0