mail.curtcpa.com has no CNAME records.
Question and response
Question
dig mail.curtcpa.com. NS
Answer
The response has no answer records.
Authority
curtcpa.com. 2848 SOA NS61.WORLDNIC.com. namehost.WORLDNIC.com. 125031211 10800 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0