spf.flexmail.net has no CNAME records.
Question and response
Question
dig spf.flexmail.net. NS
Answer
The response has no answer records.
Authority
flexmail.net. 2555 SOA ns3.combell.net. hostmaster.flexmail.net. 1764922866 10800 3600 604800 40000
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0