mxbackup.mad.interhost.com has no MX records.
Question and response
Question
dig mxbackup.mad.interhost.com. MX
Answer
The response has no answer records.
Authority
mad.interhost.com. 3600 SOA ns.interhost.com. hostmaster.mad.interhost.com. 2026022439 7200 1800 1209600 10799
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0