smtp3c.sendmetric.com has no CNAME records.
Question and response
Question
dig smtp3c.sendmetric.com. NS
Answer
The response has no answer records.
Authority
sendmetric.com. 1800 SOA hazel.ns.cloudflare.com. dns.cloudflare.com. 2398054279 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0