mail.flashstart.com has no CNAME records.
Question and response
Question
dig mail.flashstart.com. NS
Answer
The response has no answer records.
Authority
flashstart.com. 310 SOA ns11.domaincontrol.com. dns.jomax.net. 2026021800 28800 7200 604800 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0