ns4.mainloop.net has no CNAME records.
Question and response
Question
dig ns4.mainloop.net. NS
Answer
The response has no answer records.
Authority
mainloop.net. 491 SOA ns1.mainloop.net. hostmaster.mainloop.net. 3959 600 100 604800 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0