As far as I understand, a CNAME record is served to retrieve only the A record of its destination. E.g.:
www.example.com CNAME domain.com
Here the DNS resolver will search for the A record (IP address) of domain.com.
It is not allowed by RFC to use the CNAME record for the bare domain name, although, technically, it is possible. Like here:
example.com CNAME domain.com
example.com MX mail.example.com (MX will not work in this case)
However, I still don't understand how this record conflicts with other records like MX from the technical point of view and why the A record does not conflict, for instance. I guess I've missed something.
By the way, there are CNAME Flattening, ANAME or ALIAS records that have different implementations than the standard CNAME and they do not conflict with other records.
Could you explain?