ns4.netskope.com has no MX records.
Question and response
Question
dig ns4.netskope.com. MX
Answer
The response has no answer records.
Authority
netskope.com. 60 SOA ns1.netskope.com. hostmaster.netskope.com. 1772442355 3600 600 604800 60
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0