OSEC

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Subject: Re: "resubmission" feature
From: Wietse Venema (wietseporcupine.org)
Date: Mon Jul 10 2000 - 11:49:49 CDT

Lutz Vieweg:
> Wietse Venema wrote:
>
> > > The simple and sufficient criterion for me to decide whether the
> > > sender is allowed to place such a "resubmission" is the IP-address
> > > of the peer contacting the SMTP server. Only local ones would be
> > > allowed.
> >
> > Eh? You are assuming that the entire mail infrastructure consists
> > of one server.
>
> It currently does and probably will for quite some time.

Forgive me, as the author of a mail system I have to think a few
steps ahead of the immediate problem.

> > Your firewall relay has a local IP address, too,
> > but that does not mean that all mail from the firewall comes from
> > a local sender.
>
> But that's a known address. I could restrict the possibility to
> issue resubmissions to local addresses _excepting_ of course any other
> relay that might exist.

And such gotcha's immediately make a feature much less useful.

> > > But how can an external pipe transport find out this peer address -
> > > is there any header postfix adds that I could rely on? Maybe because
> > > it is in a certain position?
> >
> > The client IP address is not sufficient for finding out if a user
> > is local.
>
> Of course there would be better solutions - such as using a x509 client
> certificate to authenticate the sender. If there's enough time one day
> to implement that, I'll happily do that.
>
> But assuming that currently checking the IP of the SMTP partner is sufficient
> for us - is there a way for an external pipe transport to get it?

Not currently, although I intend to ship source attributes along with
a queue file so they can be used in $name expansions. More opportunity
for data-driven security holes.

On the other hand, this feature could very well be implemented
outside the MTA, for example in the mail delivery agent (cyrus does
a lot of stuff already) or even on the mail user agent side.

        Wietse