mail.acelerate.net has no MX records.
Question and response
Question
dig mail.acelerate.net. MX
Answer
The response has no answer records.
Authority
acelerate.net. 600 SOA ns1.acelerate.com. dnsadmin.acelerate.com. 2015052200 21600 3600 604800 600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0