smtp688.us.confirmit.com has no CNAME records.
Question and response
Question
dig smtp688.us.confirmit.com. NS
Answer
The response has no answer records.
Authority
confirmit.com. 15626 SOA udns1.cscdns.net. hostmaster.cscdns.net. 2018082972 10800 1800 1814400 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0