dc2b.sendmetric.com has no MX records.
Question and response
Question
dig dc2b.sendmetric.com. MX
Answer
The response has no answer records.
Authority
sendmetric.com. 1800 SOA hazel.ns.cloudflare.com. dns.cloudflare.com. 2396883662 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0