mx01.routing.net has no CNAME records.
Question and response
Question
dig mx01.routing.net. NS
Answer
The response has no answer records.
Authority
routing.net. 7 SOA ns1.routing.net. hostmaster.routing.net. 2026021801 14400 3600 604800 900
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0