mx.jb-mode.com has no CNAME records.
Question and response
Question
dig mx.jb-mode.com. NS
Answer
The response has no answer records.
Authority
jb-mode.com. 3439 SOA dns.jb-mode.com. hostmaster.jb-mode.com. 1234388789 43200 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0