grtg.net has no MX records.
Question and response
Question
dig grtg.net. MX
Answer
The response has no answer records.
Authority
grtg.net. 900 SOA nsa.vtx1.net. fieldopadmin.vtx1.net. 11 10800 3600 2419200 900
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0