[Exim] tricky routing-problem

Hi all,

I have a routing-problem I can't cope with. Probably my fault, not
exims. ;-)

I have a central mailserver who accepts everything for "domain" as local
mail and relays mail for dep1.domain to dep6.domain. Mail arrives for
domain and a LDAP-lookup is used to find out wether it is local mail or
if it should be forwarded to one of the departments. Works fine.

But sometimes I get mail for "someone@???" which arrives at my
central server and is passed to dep1.domain without a LDAP-lookup. But
at dep1.domain some users moved to the central mail-server some weeks
ago, so sometimes LDAP yields that the mail has to be sent back to the
central server. But the central server sees "Hey, it's for dep1.domain,
that's not local so I just relay to dep1.domain". Mailloop.

Right now the central server is the only one running exim, otherwise I
would try to enable adress-rewriting on the depX.domain-mail-servers to
solve this problem. But I'm not sure that would work...

So what can I do? I could put all my depX.domain in "local_domains" to
accept the mail and run an LDAP-lookup. But LDAP yields
"someone@???" for "someone@domain" which would again be
considered local... BANG.
I could try adress-rewriting. Rewrite "someone@???" to
"someone@domain". But rewriting not only happens, when a mail arrives
but when I do alias- or LDAP-lookups too. BANG.

Any ideas how I could try to handle this situation? When creating my
setup I didn't expect external mail for "someone@???".

--
CU,
Patrick.
"Never run on auto-pilot" - The Pragmatic Programmer