I don't want to highjack this thread, but I have a similar quandary in
regards to Exchange servers. We have 9 Exch servers, and for both
historical and practical reasons (not wanting to support 2 extra Exch
bridgehead boxes), we would like Postfix to deliver to users homed on
each server individually.

Naturally, all the users have the same @example.com address. Their
accounts are located on exch1.domain.example.com,
exch2.domain.example.com etc. The Postfix server will be living in the
example.com TLD. The user accounts do NOT include an SMTP address of
the form "user@exch1.domain.example.com".

I have no problems with extracting all the users' SMTP addresses, their
usernames and their home MDB servers from the AD via Perl and SCPing it
to the Postfix server in whatever format and number of maps that would
be appropriate.

I am guessing that it's a combination of virtual mailbox domains and
transport maps, but I don't know how to glue it together, if indeed,
it's possible. Multiple non-exchange servers in other subdomains are
similarly affected.

Other than LDAP lookups, I assume it's a similar problem to the
original post. If not, my apologies, and I'll start a new thread.