ietf-smtp
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MX lookup error handling change

2008-05-08 05:19:42

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  <dot(_at_)dotat(_dot_)at>  http://dotat.at/
FAIR ISLE: SOUTHEASTERLY 3 OR 4, INCREASING 5 OR 6 LATER. SLIGHT OR MODERATE.
FAIR. GOOD.

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