mailserver.acelerate.com has no CNAME records.
Question and response
Question
dig mailserver.acelerate.com. NS
Answer
The response has no answer records.
Authority
acelerate.com. 2752 SOA ns1.acelerate.com. dnsadmin.acelerate.com. 2025060400 7200 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0