[Exim] central mx distributing to 10 Mail-Server

Hi all,

I apologize for the bad subject, but I don't know how
to describe my problem with just one short sentence. I read the FAQ,
the list-archive of the last two or three month and I tried to search
the archive with some keywords, but I failed. The example-configurations
didn't help either.
I expected to find my problem in the list-archive or somewhere else in
the documentation, so if you could give me a hint where to find
information, it would be ok...

So, now the problem.

mail.domain is the mail-relay of my domain. department1.domain to
department10.domain are mail-servers of each department.
local-part@domain gets to mail.domain, there a lookup takes place in order to
find out which mail-server is responsible for delivering the message.
Then the message is forwarded to the appropriate department-mail-server.
Of course, local-part is unique in the domain,
Every department-mail-server has a complete table, so mail from alice
(department 1) is send directly to bob (department 7) without passing
mail.domain

This setup can't be changed, due to politics "let every department have
its own mail-server".

I would like to change one of the department-mailservers from PP to
exim. But how can I have exim do a lookup like "bob@domain, lets see...
no, he is not a local user... lookup in other table... bob belongs to
department7, so I send it directly to department7.domain"

Should I put it in a director, assuming that local-part is local and
perhaps finding out that it is remote after all? Or using a router,
assuming it is a remote adress and perhaps finding out that it is in
fact local?

My first attempt is, to put it all in an alias-file.
#examle-alias-file
first.lastname: me
admin: me
me: me@???

Of course I would get a 5000 lines alias-file.
But using a hash-table, it would probably be ok...
BTW, assume that example-alias-file was installed on department7.domain.
Would it work or would I have to exclude the last line to prevent loops?

BTW, in a small test-installation everything works fine with a big
alias-file. Did I overlook something? What would more experienced exim
users suggest?

Wow, this mail got rather long, sorry.

--
CU,
Patrick

"Funny. Just when you think life can't get any worse, it suddenly does."
Marvin