core.knownhost.net has no MX records.
Question and response
Question
dig core.knownhost.net. MX
Answer
The response has no answer records.
Authority
knownhost.net. 3600 SOA ns1.knownhost.com. dns.knownhost.com. 2021122300 3600 1800 1814400 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0