mail.ports.net has no CNAME records.
Question and response
Question
dig mail.ports.net. NS
Answer
The response has no answer records.
Authority
ports.net. 2039 SOA ns1.p201.dns.oraclecloud.net. registry.ports.net. 2026010500 3600 1800 2419200 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0