cp.rltx.net has no MX records.
Question and response
Question
dig cp.rltx.net. MX
Answer
The response has no answer records.
Authority
rltx.net. 1800 SOA osmar.ns.cloudflare.com. dns.cloudflare.com. 2397010359 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0