mxbackup.mad.interhost.com has no CNAME records.
Question and response
Question
dig mxbackup.mad.interhost.com. NS
Answer
The response has no answer records.
Authority
mad.interhost.com. 3360 SOA ns.interhost.com. hostmaster.mad.interhost.com. 2026022430 7200 1800 1209600 10799
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0