SM wrote:
When a domain name associated with an MX RR is looked up and
the associated data field obtained, the data field of that
response MUST contain a fully-qualified domain name. That
fully-qualified domain name, when queried, MUST return at
least one address record (e.g., A or AAAA RR) that gives the
IP address of the SMTP server to which the message should
be directed. Any other response, specifically including a
value that will return a CNAME record when queried, lies
outside the scope of this standard. The prohibition on CNAME
RRs is discussed in more detail in RFC 2181, Section 10.3 [29].
That looks like a good compromise to me.
I'd remove the word 'specifically', it makes me read the statement
more than once to be sure of its meaning, and is probably redundant.
Mark