mail.efolder.net has no CNAME records.
Question and response
Question
dig mail.efolder.net. NS
Answer
The response has no answer records.
Authority
efolder.net. 1593 SOA ns2.efscloud.net. domainadmin.efolder.net. 61 14400 600 3600000 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0