mail.o4scloud.com has no CNAME records.
Question and response
Question
dig mail.o4scloud.com. NS
Answer
The response has no answer records.
Authority
o4scloud.com. 800 SOA nsauth1.pinkzuid.nl. hostmaster.pinkzuid.nl. 2024030100 28800 7200 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0