sitsanetworks.net has no MX records.
Question and response
Question
dig sitsanetworks.net. MX
Answer
The response has no answer records.
Authority
sitsanetworks.net. 10800 SOA ns1.lzsnet.com.ar. postmaster.lzsnet.com.ar. 2013022603 28800 900 2419200 10800
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0