mmmail01.activetrail.com has no MX records.
Question and response
Question
dig mmmail01.activetrail.com. MX
Answer
The response has no answer records.
Authority
activetrail.com. 3600 SOA dns1.p07.nsone.net. hostmaster.nsone.net. 1628672097 3600 600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0