cust-spf.primerelay.net has no CNAME records.
Question and response
Question
dig cust-spf.primerelay.net. NS
Answer
The response has no answer records.
Authority
primerelay.net. 108 SOA ns1.primerelay.net. hostmaster.primerelay.net. 2024102401 15800 3600 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0