[Exim] Simple(?) newbie problem ...

Hi,

please take a look at my (simple?) problem:

Let's say i have a domain called foo.org and i get mail from there by
using fetchmail and deliver them to my localexim. I configured exim
saying that foo.org is a local domain (That's Ok isn't it?) On my
exim-server, i created login accounts for all users with an
email-address at foo.org. When i send an email to somebody@??? (
suppose he is an external user that takes uses the smtp and pop service
of my provider hosting foo.org ) exim thinks that the user has to be
local, tries to lookup somebody, but since there is no shell account for
him, exim says something like unknown user.

Now my questions:

1. How can i avoid creating a user account on the server running exim
for each user?

2. How can i configure exim, so that emails for somebody@??? (and
all other not local users) are delivered?

I googled a bit, but could not find a hint. Could somebody give me a hint?

I'am using exim 3.35 on Debian Woody.

Regards,
Kamran Remin