On Sun, Dec 07, 2003 at 11:04:11AM +0000, Tim Jackson wrote:
> Hi Philip, on Fri, 5 Dec 2003 14:01:45 +0000 (GMT) you wrote:
>
> > On Fri, 5 Dec 2003, Tim Jackson wrote:
>
> [on delivering mail to postmaster@[IP]]
>
> > > In this context, I think it *is* meaningful to want to deliver mail
> > > to a specific box, if one knows that it is running an MTA. (And if it
> > > isn't, the mail bounces - no problem).
> > Why? Can you really assume that deliving to a specific box is going to
> > get to the (logical) person you are trying to contact?
>
> If the MTA on IP 1.2.3.4 is playing up, I think the closest systematic
> assumption I can make of trying to reach the postmaster there is
> "postmaster@[ip]". I don't think this is making any more assumptions than
> picking addresses based on reverse DNS fragments, IPWHOIS or other
> sources which are themselves not infallible.
My problem with IP literals is that (eg) postmaster@[myrelaymtaip] doesn't
exist in the first place. Note: I'm not saying that postmaster@mydomain
does not exist; it most certainly does. However, because the externally
reachable MTA purely provides filtering and routing with _zero_ local
users, it doesn't have a postmaster address of its own. It doesn't
even have any local domains as such. (It has a fixed set of domains
which it does relay for, and that's all.)
This means that although "myrelaymtaip" runs a SMTP server, but any mail
to its ip literal will be rejected.
Now, the interesting thing is that RFC2821 section 4.5.1 says:
Any system that includes an SMTP server supporting mail relaying or
delivery MUST support the reserved mailbox "postmaster" as a case-
insensitive local name. This postmaster address is not strictly
necessary if the server always returns 554 on connection opening (as
described in section 3.1). The requirement to accept mail for
postmaster implies that RCPT commands which specify a mailbox for
postmaster at any of the domains for which the SMTP server provides
mail service, as well as the special case of "RCPT TO:<Postmaster>"
(with no domain specification), MUST be supported.
Since my MTA does not provide mail service for the domain [myrelaymtaip],
but does for "mydomain", where it accepts postmaster as a local part,
and it accepts <postmaster> on its own, I believe that I'm fully
compliant with this RFC section.
Maybe someone needs to update RFC2821 to include IP literal postmaster
contact information, and then maybe we should all follow and provide
such a mailbox. 8)
--
Russell King
Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/
maintainer of: 2.6 PCMCIA - http://pcmcia.arm.linux.org.uk/
2.6 Serial core
