136.6.21.216.forestracks.net has no MX records.
Question and response
Question
dig 136.6.21.216.forestracks.net. MX
Answer
The response has no answer records.
Authority
forestracks.net. 1800 SOA evan.ns.cloudflare.com. dns.cloudflare.com. 2398592720 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0