dcv.digicert.com has no MX records.
Question and response
Question
dig dcv.dcvcheck.com. MX
Answer
The response has no answer records.
Authority
dcvcheck.com. 180 SOA ns10.digicertdns.com. dns.digicertdns.com. 2016711042 43200 3600 1209600 180
Additional
. 0 OPT ; payload 1280, xrcode 0, version 0, flags 0