xmx.interhost.com has no CNAME records.
Question and response
Question
dig xmx.interhost.com. NS
Answer
The response has no answer records.
Authority
interhost.com. 3101 SOA ns.interhost.com. hostmaster.mad.interhost.com. 2026021050 7200 1800 1209600 10799
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0