This (reparagraphing) change has been tentatively made to -08.
I can also change the final sentence to read "The DNS DATA field
associated with the lookup of an MX record must not contain a
domain that, in turn, is associated with a CNAME record" or
something to that general effect if people are convinced it
would be more clear rather than more confusing.
john
--On Thursday, 21 February, 2008 11:16 -0500 Tony Hansen
<[EMAIL PROTECTED]> wrote:
>
> Alessandro Vesely wrote:
> >
> > Derek J. Balling wrote:
> >> I know this may be a dead horse, but...
> >> "The result of an MX lookup MUST NOT be a CNAME."
> >> Can this *please* be slightly reworded? "The RR value of
> an MX
> >> lookup..." perhaps?
> >
>> It is the compound "MX lookup" that generates ambiguity, as
>> it is used to indicate the initial lookup of the domain name.
>> Actually, that's what the whole first paragraph in 5.1 is
>> talking about. If it were considered a minor change, I'd
>> propose moving that sentence to the end of the next
>> paragraph, where its rationale can be grasped more easily.
>
> <techie hat on>
>
> I'm thinking that the problem really lies in the paragraph
> being so long and covering multiple steps. If it were split
> apart like this, I think it would be more obvious where each
> statement applies in the flow:
>
> Once an SMTP client lexically identifies a domain to which
> mail will
> be delivered for processing (as described in sections
> Section 2.3.5
> and Section 3.6), a DNS lookup MUST be performed to
> resolve the
> domain name (RFC1035 [6]). The names are expected to be
> fully-
> qualified domain names (FQDNs): mechanisms for inferring
> FQDNs from
> partial names or local aliases are outside of this
> specification.
> Due to a history of problems, SMTP servers used for initial
> submission of messages SHOULD NOT make such inferences
> (Message
> Submission Servers [41] have somewhat more flexibility) and
> intermediate (relay) SMTP servers MUST NOT make them.
>
> The lookup
> first attempts to locate an MX record associated with the
> name. If a
> CNAME record is found instead, the resulting name is
> processed as if
> it were the initial name. If no MX records are found, but
> an address
> RR (i.e., either an IPv4 A RR or an IPv6 AAAA RR, or their
> successors) is found, the address RR is treated as if it
> was
> associated with an implicit MX RR, with a preference of 0,
> pointing
> to that host.
>
> If one or more MX RRs are found for a given name, SMTP
> systems MUST NOT utilize any address RRs associated with
> that name
> unless they are located using the MX RRs; the "implicit
> MX" rule
> above applies only if there are no MX records present. If
> MX records
> are present, but none of them are usable, this situation
> MUST be
> reported as an error. The result of an MX lookup MUST NOT
> be a
> CNAME.
>
> </techie hat off>
>
> Tony Hansen
> [EMAIL PROTECTED]
>
