ns3.gtt.net has no MX records.
Question and response
Question
dig ns3.gtt.net. MX
Answer
The response has no answer records.
Authority
gtt.net. 1800 SOA betty.ns.cloudflare.com. dns.cloudflare.com. 2397096670 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0