ns2.arpa.networklayer.com has no MX records.
Question and response
Question
dig ns2.arpa.networklayer.com. MX
Answer
The response has no answer records.
Authority
networklayer.com. 300 SOA ns1.softlayer.com. root.softlayer.com. 2025103100 7200 600 1728000 300
Additional
. 0 OPT ; payload 1280, xrcode 0, version 0, flags 0