pmx1.epsl1.com has no CNAME records.
Question and response
Question
dig pmx1.epsl1.com. NS
Answer
The response has no answer records.
Authority
epsl1.com. 3143 SOA a8-64.akam.net. netadmin.epsilon.com. 2015060577 1800 120 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0