ns4.mailkit.net has no CNAME records.
Question and response
Question
dig ns4.mailkit.net. NS
Answer
The response has no answer records.
Authority
mailkit.net. 2471 SOA ns1.mailkit.net. postmaster.mailkit.net. 2026030501 28800 300 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0