mx.umbler.com has no CNAME records.
Question and response
Question
dig mx.umbler.com. NS
Answer
The response has no answer records.
Authority
umbler.com. 60 SOA umblerdns03.westeros.local. admin.umbler.com. 2016065091 60 900 345600 60
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0