The alphabetic sort of users and the configuration was just an example.
What I really need is keep a certain number of users in one manchine, and the others in another, under the same domain name.
In my real case, the environment is composed of 1 qmail and 1 exchange server.
some users are in the qmail server and the others in the exchange server, and there is not possibilty to change this configuration.
I'd try something like this: Set the MX to the qmail server. Set up a remote catchall account on the exchange server: so all non-existant users on the qmail servers get "forwarded" to the catchall on the exchange server. (I dont know about the details of an exchange server, but there should be something similiar to procmail or maildrop, where you can check the header of the incoming mail and find out the original recipient.) Copy/Forward to the original recipients' mailbox on the exchange server.
I had to do something similiar with one qmail and one sendmail server.
--franz
