mail.grumpyminx.com has no CNAME records.
Question and response
Question
dig mail.grumpyminx.com. NS
Answer
The response has no answer records.
Authority
grumpyminx.com. 582 SOA ns1.grumpyminx.com. pete.318.org.uk. 2026030500 86400 7200 3600000 172800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0