Re: [Exim] Domain literals: weighing up the arguments

[ On Tuesday, December 9, 2003 at 21:54:40 (+0000), Russell King wrote: ]
> Subject: Re: [Exim] Domain literals: weighing up the arguments
>
> On Tue, Dec 09, 2003 at 04:44:10PM -0500, Greg A. Woods wrote:
> > [ On Tuesday, December 9, 2003 at 10:14:48 (+0000), Philip Hazel wrote: ]
> > > That's a good description of the way I have always understood this.
> >
> > No, it's totally bogus.
>
> So you're going to mandate that all hosts on the internet must accept
> email, whether they are running a SMTP daemon or not, just because
> you can mail postmaster@[theiripaddress] ?

If you'd bother to read and try to understand what I've written
repeatedly in some valiant attempt to make this extremely clear to you,
you would already have known that I am not trying to mandate anything
even remotely close to that.

> This is the logical extension to the argument that postmaster@[ipliteral]
> works. Remember - one of the arguments put forward is that any host
> which can send mail should be contactable by this means so that problems
> can be reported.

You are either confusing this issue with the arguments for the "abuse"
mailbox, or perhaps you are just totally confused.


Here are some relevant quotes from the relevant RFCs which _might_ help
you to be a little less confused. Please try to read these quotes very
carefully and _very_ completely. Note that none of this is even
remotely new -- it's been the case since the very beginning of SMTP.

Every HOST which _receives_ mail _must_ have a "postmaster" mailbox, and
while "RCPT TO:<postmaster>" is allowed, the <POSTMASTER@domain> address
_MUST_ also be valid:

RFC 822 (August 13, 1982)

     6.3.  RESERVED ADDRESS

          It often is necessary to send mail to a site, without  know-
     ing  any  of its valid addresses.  For example, there may be mail
     system dysfunctions, or a user may wish to find  out  a  person's
     correct address, at that site.

          This standard specifies a single, reserved  mailbox  address
     (local-part)  which  is  to  be valid at each site.  Mail sent to
     that address is to be routed to  a  person  responsible  for  the
     site's mail system or to a person with responsibility for general
     site operation.  The name of the reserved local-part address is:

                                Postmaster

     so that "Postmaster@domain" is required to be valid.

     Note:  This reserved local-part must be  matched  without  sensi-
            tivity to alphabetic case, so that "POSTMASTER", "postmas-
            ter", and even "poStmASteR" is to be accepted.

RFC 2142 (May, 1997)

1. RATIONALE AND SCOPE

Various Internet documents have specified mailbox names to be used
when reaching the operators of the new service; for example, [RFC822
6.3, C.6] requires the presence of a <POSTMASTER@domain> mailbox name
on all hosts that have an SMTP server.


And of course "domain" may be the literal IP address of the host (in the
form originally labeled "domain-literal" in RFC 822):

RFC 821 (August, 1982):

[[ ... reordered and summarized to show just the relevant syntax ... ]]

            RCPT <SP> TO:<forward-path> <CRLF>

            <forward-path> ::= <path>

            <path> ::= "<" [ <a-d-l> ":" ] <mailbox> ">"

            <mailbox> ::= <local-part> "@" <domain>

            <domain> ::=  <element> | <element> "." <domain>

            <element> ::= <name> | "#" <number> | "[" <dotnum> "]"

         Sometimes a host is not known to the translation function and
         communication is blocked.  To bypass this barrier two numeric
         forms are also allowed for host "names".  One form is a decimal
         integer prefixed by a pound sign, "#", which indicates the
         number is the address of the host.  Another form is four small
         decimal integers separated by dots and enclosed by brackets,
         e.g., "[123.255.37.2]", which indicates a 32-bit ARPA Internet
         Address in four 8-bit fields.

(I think most everyone will agree the '#' form is deprecated, though I
have seen it used recently by those trying to exploit failures to take
this form into account for ACLs and such so either it must be carefully
rejected outright or else handled fully and properly.)


However it is only every "top level" DOMAIN used in e-mail which must
have an "abuse" mailbox:

RFC 2142 (May, 1997)

2. INVARIANTS

For well known names that are not related to specific protocols, only
the organization's top level domain name are required to be valid.
For example, if an Internet service provider's domain name is
COMPANY.COM, then the <ABUSE@???> address must be valid and
supported, even though the customers whose activity generates
complaints use hosts with more specific domain names like
SHELL1.COMPANY.COM. Note, however, that it is valid and encouraged
to support mailbox names for sub-domains, as appropriate.

--
                        Greg A. Woods

+1 416 218-0098                  VE3TCP            RoboHack <woods@???>
Planix, Inc. <woods@???>          Secrets of the Weird <woods@???>