mail.payex.com has no CNAME records.
Question and response
Question
dig mail.payex.com. NS
Answer
The response has no answer records.
Authority
payex.com. 2752 SOA ns1.p201.dns.oraclecloud.net. registry.ports.net. 2026022200 3600 600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0