[Exim] How to implement qmail-ldap like cluster/distributed …

Hi all,

I'm new to exim, and have a question: how to implement qmail-ldap
like cluster/distributed mail system?

Background:

Our company is wide-distributed: a headquarter and 15 (be growing to
25-30 at this year-end) branches. In the view of saving bandwidth and
the responding time of the server, we implement the internal email
system as a distributed system under one same domain. Each branch has
a physical server to serve all its local users. The local mail(mail sent
by one user to another in the same branch) is exchanged locally, not
transmitted thru our WAN connection.

Currentlyn our company uses qmail as our internal/external email system,
but qmail lacks management tool, such as queue cleaning, monitoring.

So we are considering to switch the mail system (mta) to exim or postfix.

The postfix can be implement to qmail-ldap like system by using "per-user
transport",but Exim has a powerful ACL control mechanism that we really
needed, so I prefer Exim.

Any one can give me some hints?

Thanks a lot,
Hunte