mail3.casscomm.com has no CNAME records.
Question and response
Question
dig mail3.casscomm.com. NS
Answer
The response has no answer records.
Authority
casscomm.com. 349 SOA ns.casscomm.com. postmaster.ns.casscomm.com. 2008041129 90 30 259200 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0