On Tue 26/Jun/2012 23:16:04 +0200 Lucio Crusca wrote:
> Alessandro Vesely wrote:
>> 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.
>
> I don't quite get why (and it's crucial I understand it before I tell the
> other domain tech contact it's his fault).
Suppose you had come into an agreement with that domain.com, so that
your server works (also) as a backup MX for them. Of course, you
would also have configured other stuff such as smtpacceptmailfor, but
how do you think Courier would be able to learn the preference number
that it is supposed to operate at?
> Could you please give me a pointer to relevant RFC about the SMTP prohibition
> you cited?
It's all in the same SMTP section that Jan cited. It is good to
understand it thoroughly (albeit not so crucial for reporting that
error.) The last paragraph of it says:
all records at that preference level and higher-numbered ones MUST be
discarded from consideration.
http://tools.ietf.org/html/rfc5321#section-5.1
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