arrow-relay.mxrouting.net has no MX records.
Question and response
Question
dig arrow-relay.mxrouting.net. MX
Answer
The response has no answer records.
Authority
mxrouting.net. 3600 SOA ns21.cloudns.net. support.cloudns.net. 2026012302 7200 1800 1209600 3600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0