mail.accountsupport.com has no CNAME records.
Question and response
Question
dig mail.accountsupport.com. NS
Answer
The response has no answer records.
Authority
accountsupport.com. 2269 SOA ns1.yourhostingaccount.com. admin.yourhostingaccount.com. 2004012601 10800 3600 700000 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0