aamelnikov
commented
2 days ago After some mailing list discussion Ted proposed the following:
OLD: 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 labels in the data that resolve to CNAMEs is discussed in more detail in RFC 2181, Section 10.3 [33].
NEW: An MX record with a CNAME as its target is a misconfiguration, as explained in RFC2181, Section 1.3 [33]. However, implementations SHOULD still process CNAME responses when received, since a significant number of servers on the internet are configured with MX records pointing to CNAMEs.
Ted Lemon wrote:
Section 5.1 doesn't say what to do with chained CNAMEs. It might be worth saying more here. A strict reading of the spec here would I think treat chained CNAMES correctly in the sense that if the target of the CNAME is treated as the initial name, then each target would be processed the same way, by first looking for a CNAME. And of course a full-service resolver will do the CNAME work for the SMTP client. So perhaps clarifying that the "resulting name" is the result of fully following the CNAME as described in RFC1035 section 7.1.