mx.tuff-e.com has no CNAME records.
Question and response
Question
dig mx.tuff-e.com. NS
Answer
The response has no answer records.
Authority
tuff-e.com. 3492 SOA dns.tuff-e.com. hostmaster.tuff-e.com. 1436067614 43200 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0