mail.simonstl.com has no CNAME records.
Question and response
Question
dig mail.simonstl.com. NS
Answer
The response has no answer records.
Authority
simonstl.com. 2353 SOA NS85.WORLDNIC.com. namehost\@WORLDNIC.com. 124112107 10800 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0