mib.mailinblack.com has no MX records.
Question and response
Question
dig mib.mailinblack.com. MX
Answer
The response has no answer records.
Authority
mailinblack.com. 10800 SOA ns1.gandi.net. hostmaster.gandi.net. 1771835125 10800 3600 604800 10800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0