ftmail2.flexential.com has no CNAME records.
Question and response
Question
dig ftmail2.flexential.com. NS
Answer
The response has no answer records.
Authority
flexential.com. 3386 SOA ns1.peak10.com. dev-notices.peak10.com. 2018011800 3600 1200 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0