smtp1.slc.efscloud.net has no CNAME records.
Question and response
Question
dig smtp1.slc.efscloud.net. NS
Answer
The response has no answer records.
Authority
efscloud.net. 737 SOA ns1.efscloud.net. efscloud.net.domainsbyproxy.com. 394 600 300 3600000 900
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0