mail.tuart.netdesignhost.com has no CNAME records.
Question and response
Question
dig mail.tuart.netdesignhost.com. NS
Answer
The response has no answer records.
Authority
tuart.netdesignhost.com. 5401 SOA ns1.netdesignhost.com. contact.netdesignhost.com. 1299256289 10800 3600 604800 10800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0