mx2.ip-only.net has no CNAME records.
Question and response
Question
dig mx2.ip-only.net. NS
Answer
The response has no answer records.
Authority
ip-only.net. 2072 SOA a.ns.ip-only.net. registry.ip-only.net. 2026021100 14400 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0