mailfilter-se3-1.rackhosting.com has no CNAME records.
Question and response
Question
dig mailfilter-se3-1.rackhosting.com. NS
Answer
The response has no answer records.
Authority
rackhosting.com. 523 SOA dns1.rackhosting.com. drift.rackhosting.com. 1773063859 10800 3600 604800 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0