smtp4f.sendmetric.com has no CNAME records.
Question and response
Question
dig smtp4f.sendmetric.com. NS
Answer
The response has no answer records.
Authority
sendmetric.com. 41 SOA hazel.ns.cloudflare.com. dns.cloudflare.com. 2396883662 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0