mx002.rexx-systems.com has no CNAME records.
Question and response
Question
dig mx002.rexx-systems.com. NS
Answer
The response has no answer records.
Authority
rexx-systems.com. 300 SOA rexx-systems.com. root.rexx-systems.com. 2026030203 3600 3600 604800 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0