mx-asgard.mailinblack.com has no CNAME records.
Question and response
Question
dig mx-asgard.mailinblack.com. NS
Answer
The response has no answer records.
Authority
mailinblack.com. 9206 SOA ns1.gandi.net. hostmaster.gandi.net. 1772668800 10800 3600 604800 10800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0