> Let me rephrase the question more generally. Suppose there were
> three local users; alan, ben, and charles. Can exim be configured
> so that if ben wants to send mail to charles he uses whatever his
> MUA to enter 'charles' and the mail stays here; presumable charles
> could sent messages to 'alan' and 'ben' and the mail would stay
> here. But any other message, with a more complete address -- way to
> superman@???, would get sent off by exim to krypton.org and to
> Superman's mbox(we know Superman doesn't use Maildir, don't we?)
>
> I bet there is a way of doing this with exim, and I bet you and lots
> of others here know how.
The simple answer is that Exim can certainly do this but it's unlikely
that anyone is going to have a canned configuration to do this that they
can dump out here.
The best way to think of Exim in its basic state is that it is not a
mailer so much as a mailer construction kit. To actually use Exim as a
MTA, you build whatever actual specific mailer you need out of it by
designing and programming a series of both ACL rules and routers (and
sometimes transports). Any existing Exim configuration (including the
'generic' configurations supplied with eg the Debian and Ubuntu packaged
versions of Exim) is the outcome of such a design and building process,
with as much or as little genericness as desired and possible.
The primary ingredient of Exim as a mailer construction kit is Exim
routers. For sophisticated Exim usage, you want to think about routers
as (conditional) steps or decision points in a peculiar programming
language. Each router implements certain decisions and handles certain
addresses under certain circumstances; how you order your collection of
routers then determines how addresses flow through the overall system
to achieve effects that you want.
In your particular case, you would have more or less a setup with some
routers that recognize 'local' users on the current machine and deliver
their mail, and then another router that sends all other krypton.org
addresses off to the appropriate mail server.
- cks
[I wrote about this approach at more length and in perhaps a more
readable way here:
http://utcc.utoronto.ca/~cks/space/blog/sysadmin/EximRouterPower
if people are interested in it. There's also
http://utcc.utoronto.ca/~cks/space/blog/sysadmin/EximMailerKit
on the general mindset of Exim as a mailer construction kit.
]
