mx-express-mailing.omerdecugis.com has no CNAME records.
Question and response
Question
dig mx-express-mailing.omerdecugis.com. NS
Answer
The response has no answer records.
Authority
omerdecugis.com. 928 SOA erin.ns.cloudflare.com. dns.cloudflare.com. 2397428573 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0