relay.jetsmtp.net has no MX records.
Question and response
Question
dig relay.jetsmtp.net. MX
Answer
The response has no answer records.
Authority
jetsmtp.net. 1800 SOA melina.ns.cloudflare.com. dns.cloudflare.com. 2396931151 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0