1683928c7.spf2.netcorecloud.net has no MX records.
Question and response
Question
dig 1683928c7.spf2.netcorecloud.net. MX
Answer
The response has no answer records.
Authority
netcorecloud.net. 180 SOA ns11.constellix.com. dns.constellix.com. 2015010640 43200 3600 1209600 180
Additional
. 0 OPT ; payload 1280, xrcode 0, version 0, flags 0