x.incapdns.net has no MX records.
Question and response
Question
dig x.incapdns.net. MX
Answer
The response has no answer records.
Authority
incapdns.net. 300 SOA ns1.incapdns.net. hostmaster.incapsula.com. 5 3600 600 604800 60
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0