--On Monday, 26 November, 2007 02:42 +1100 Chris Wright
<[EMAIL PROTECTED]> wrote:
> Hi John,
> My name is Chris, I am CTO of AusRegistry the registry
> operator of the .au cctld. I have been doing some research on
> the SMTP protocol lately and have come up with something that
> I guess is a potential ambiguity in the SMTP protocol defined
> in RFC2821 you authored (if I am remembering my BNF
> correctly). Any clarification you can shed on the matter would
> be greatly appreciated.
>
> In section 2.3.5 of the RFC you define the domain name part of
> an email address as being "one or more dot-separated
> components" (I have reproduced it below to save you having to
> go and find it). Further down in section 4.1.2 your grammar
> describes the domain as being:
>
> Domain = (sub-domain 1*("." sub-domain)) / address-literal
>
> Which (If I am hopefully remembering correctly means a
> sub-domain followed by 1 or more "." sub-domain combinations.
> This appears to be in contradiction to the paragraphs of 2.3.5.
>
> I have come up against it because I am looking at the
> possibilities of having email addresses under a TLD eg.
> [EMAIL PROTECTED] or [EMAIL PROTECTED], which would presumably be legal given
> that au or com is a fully qualified domain name (when you put
> the dot on the end). It appears most email software doesn't
> support this :(
>
> Could you clarify firstly my interpretation and secondly the
> intent of the RFC, would be greatly appreciated.
>
> Thanks
>
> From Section 2.3.5 of RFC2821
>
> A domain (or domain name) consists of one or more
> dot-separated components. These components ("labels" in
> DNS terminology [22]) are restricted for SMTP purposes to
> consist of a sequence of letters, digits, and hyphens drawn
> from the ASCII character set [1]. Domain names are used as
> names of hosts and of other entities in the domain name
> hierarchy. For example, a domain may refer to an alias (label
> of a CNAME RR) or the label of Mail eXchanger records to be
> used to deliver mail instead of representing a host name.
> See [22] and section 5 of this specification.
>
> The domain name, as described in this document and in [22],
> is the entire, fully-qualified name (often referred to as
> an "FQDN"). A domain name that is not in FQDN form is no
> more than a local alias. Local aliases MUST NOT appear in
> any SMTP transaction.
>
>
> From Section 4.1.2
>
> Domain = (sub-domain 1*("." sub-domain)) / address-literal
Hi Chris,
There is a revision of 2821 in progress. The current draft is
draft-klensin-rfc2821bis-06.txt and discussion is occurring on
the ietf-smtp list (copied on this note to expose your question
and comments on the list).
The question of whether an address of the form [EMAIL PROTECTED] was
actively discussed some months ago, and the ICANN ccNSO and gNSO
were polled on the question. The (few) responses we got back
from the latter can, I think, be fairly summarized as "no one
cared very much", something you can verify with Chris Disspain
if you like.
The difficulty with TLD-only addresses is that the mail
protocols do not permit that trailing dot. Discussion over the
last year concluded that the backwards-compatibility issues that
would be raised by changing that are far more problematic than
the change might be worth. So, if one has a one-component name,
there is some difficulty in distinguishing it lexically from an
abbreviation (not permitted on the wire, but common in local
systems). For that reason and regardless of what is done with
the standard, you should anticipate difficulties with some mail
user agents in handling the address.
However, while one must be cautious, there seems to be no reason
to prohibit a TLD from being used as an MX record and receiving
mail, so the revision draft has been changed to explicitly
permit that form. In the working draft I've further modified
that uncomfortable sentence in 2.3.5 but the text (and syntax)
of -06 clearly permit what you want to do.
regards,
john
