mail.captiontext.com has no CNAME records.
Question and response
Question
dig mail.captiontext.com. NS
Answer
The response has no answer records.
Authority
captiontext.com. 2788 SOA ns1.viawest.net. hostmaster.viawest.net. 7 43200 7200 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0