mail100.siidc.net has no MX records.
Question and response
Question
dig mail100.siidc.net. MX
Answer
The response has no answer records.
Authority
siidc.net. 60 SOA ns1.siidc.net. root.ns1.siidc.net. 2010050482 10800 1800 4233600 21600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0