o4.mailservice.namecheap.com has no CNAME records.
Question and response
Question
dig o4.mailservice.namecheap.com. NS
Answer
The response has no answer records.
Authority
namecheap.com. 1067 SOA edns.registrar-servers.com. support.namecheap.com. 1770891650 28800 7200 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0