ns4.goskope.com has no MX records.
Question and response
Question
dig ns4.goskope.com. MX
Answer
The response has no answer records.
Authority
goskope.com. 300 SOA ns1.goskope.opskope.com. hostmaster.nsone.net. 1771955992 3600 600 604800 300
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0