ns3.mailkit.com has no CNAME records.
Question and response
Question
dig ns3.mailkit.com. NS
Answer
The response has no answer records.
Authority
mailkit.com. 3566 SOA ns1.mailkit.com. hostmaster.mailkit.com. 2026030501 3600 300 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0