On 25-Jan-2009, at 03:44 , Al Stu 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 domain name. That 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."Correct. And when a that domain name is a CNAME pointing to an A RR the query returns not only the alias but also the real name and the IP address from the A RR. Thus meeting the requirements to "return at least one address record (e.t., A or AAAA RR)". But yet ISC seems to find it necessary to throw a message that it is "illegal", when it clearly is not.
You've added an additional step in your second paragraph that is prohibited by the section you quoted in the first. The section from the RFC describes a situation where A is queried for and an MX record pointing to B is returned. When B is queried for, an address record MUST be the answer. The situation you have described is that A is queried for resulting in an MX record pointing to B. When B is queried for, a CNAME pointing to C is returned, and that when C is queried an address record is returned. Do you see the difference?
The RFCs are quite clear that CNAMEs are not permitted in the RDATA for an MX.
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