On Tue 26/Jun/2012 13:14:34 +0200 Jan Ingvoldstad wrote: > On Tue, Jun 26, 2012 at 12:52 PM, Sam Varshavchik > <mr...@courier-mta.com <mailto:mr...@courier-mta.com>> wrote: > > There are no prescribed means for handling bad DNS data. If DNS is > wrong, one cannot have any expectation that it will work in any > particular way, even if some parts of it are correct. > > That's not quite correct, there are prescribed means for handling bad > DNS data in the context of Internet mail delivery.
> http://tools.ietf.org/html/rfc5321#section-5 > > To put it briefly: it would appear that the RFC authors think that the > good old "be tolerant in what you accept" principle still applies, and > it would not be unreasonable for an MTA to skip a broken MX record and > try the other record(s), if any. I'd be curious to know where would that tolerance be expressed in the section you refer. I'd guess because it says: If MX records are present, but none of them are usable, this situation MUST be reported as an error. Thus, since in the above case one of them seems to be usable, one can derive that it is not mandatory to report that as an error. However, the next paragraph says clearly what to expect: 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 [...] lies outside the scope of this Standard. > However, it would perhaps not be unreasonable to say "bah, screw you > guys, I'm going home" either. Indeed. For example, Lucio's server could have matched the bad MX 20 of domain.com, unable to recognize its own IP address because it sits behind a NAT, and unable to recognize its own name since the DNS hid it. If it had used the good MX record by default, it would have violated the SMTP prohibition to relay to a host at the same preference level. -- ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ courier-users mailing list courier-users@lists.sourceforge.net Unsubscribe: https://lists.sourceforge.net/lists/listinfo/courier-users
