ns1.theplanet.com has no MX records.
Question and response
Question
dig ns1.theplanet.com. MX
Answer
The response has no answer records.
Authority
theplanet.com. 900 SOA ns1.softlayer.com. root.softlayer.com. 2024101000 7200 600 1728000 900
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0