Quoting the text from rfc2821bis-09, Section 5.1:
"The lookup first attempts to locate an MX record associated with the
name. If a CNAME record is found instead, the resulting name is
processed as if it were the initial name. If no MX records are
found, but an address RR ... is found, the address RR is treated ...
Sorry for distraction, I know this has been closed previously.
Reading the statement on CNAME again, lets me believe that
it could still be misunderstood if one really wants to.
I'd propose the statement to start with the same wording
as the next statement on RR, i.e.
If a CNAME record is found instead,
If no MX records are found, but a CNAME record is found instead,