mx.mymailwall.com has no CNAME records.
Question and response
Question
dig mx.mymailwall.com. NS
Answer
The response has no answer records.
Authority
mymailwall.com. 243 SOA ns3.domaindiscount24.net. tech.key-systems.net. 2025105833 10800 3600 604800 28800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0