sysmail.siidc.com has no NS records.
NS records for this zone are defined at siidc.com.
NS records for this zone are defined at siidc.com.
Question and response
Question
dig sysmail.siidc.com. NS
Answer
The response has no answer records.
Authority
siidc.com. 60 SOA ns1.siidc.net. root.ns1.siidc.net. 2014032571 10800 1800 4233600 21600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0