ismtp.clearfly.net has no MX records.
Question and response
Question
dig ismtp.clearfly.net. MX
Answer
The response has no answer records.
Authority
clearfly.net. 1800 SOA georgia.ns.cloudflare.com. dns.cloudflare.com. 2396699710 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0