smtp4.ARIN.NET has no CNAME records.
Question and response
Question
dig smtp4.ARIN.NET. NS
Answer
The response has no answer records.
Authority
arin.net. 2809 SOA ns1.arin.net. bind.arin.net. 2021113225 10800 600 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0