smtp3j.sendmetric.com has no CNAME records.
Question and response
Question
dig smtp3j.sendmetric.com. NS
Answer
The response has no answer records.
Authority
sendmetric.com. 1475 SOA hazel.ns.cloudflare.com. dns.cloudflare.com. 2398054279 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0