ns3.sits.pro has no MX records.
Question and response
Question
dig ns3.sits.pro. MX
Answer
The response has no answer records.
Authority
sits.pro. 3600 SOA ns1.sits.pro. sd.sits.nl. 2014071783 10800 3600 1814400 7200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0