arrow.mxrouting.net has no MX records.
Question and response
Question
dig arrow.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