mail.blacknightdns.com has no MX records.
Question and response
Question
dig mail.blacknightdns.com. MX
Answer
The response has no answer records.
Authority
blacknightdns.com. 900 SOA ns.blacknightsolutions.com. sales.blacknight.ie. 2023062809 10800 3600 604800 900
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0