mx4.fuse.net has no CNAME records.
Question and response
Question
dig mx4.fuse.net. NS
Answer
The response has no answer records.
Authority
fuse.net. 93 SOA ns1.fuse.net. hostmaster.fuse.net. 3661 10800 3600 2419200 900
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0