mail.sounddsl.com has no CNAME records.
Question and response
Question
dig mail.sounddsl.com. NS
Answer
The response has no answer records.
Authority
sounddsl.com. 2010 SOA ns-1.nuoz.net. postmaster.nwnexus.com. 2022122900 7200 3600 864000 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0