ns4.instradns.com has no MX records.
Question and response
Question
dig ns4.instradns.com. MX
Answer
The response has no answer records.
Authority
instradns.com. 600 SOA ns1.instradns.com. admin.instra.com. 2014060302 2008052907 28800 7200 604800
Additional
. 0 OPT ; payload 1680, xrcode 0, version 0, flags 0