mx.efiservers.com has no CNAME records.
Question and response
Question
dig mx.efiservers.com. NS
Answer
The response has no answer records.
Authority
efiservers.com. 1739 SOA ns1.efiservers.com. root.efiservers.com. 1771340182 28800 7200 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0