sysmail.siidc.com has no CNAME records.
Question and response
Question
dig sysmail.siidc.com. NS
Answer
The response has no answer records.
Authority
siidc.com. 44 SOA ns1.siidc.net. root.ns1.siidc.net. 2014032571 10800 1800 4233600 21600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0