RFC 2821 says: If MX records are present, but none of them are usable, this situation MUST be reported as an error.
This implies that a partially broken RRset is not grounds for rejecting a message. 2821bis says: 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. Any other response, specifically including a value that will return a CNAME record when queried, lies outside the scope of this standard. This implies that it's OK to reject partially broken MX RRsets. Some deployed software already does this. Tony. -- f.anthony.n.finch <[EMAIL PROTECTED]> http://dotat.at/ FAIR ISLE: SOUTHEASTERLY 3 OR 4, INCREASING 5 OR 6 LATER. SLIGHT OR MODERATE. FAIR. GOOD.
