mail.primerelay.net has no CNAME records.
Question and response
Question
dig mail.primerelay.net. NS
Answer
The response has no answer records.
Authority
primerelay.net. 100 SOA ns1.primerelay.net. hostmaster.primerelay.net. 2024102401 15800 3600 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0