In response to "Doug Milns":
> I am running exim 3.36 serving email for virtual domains. This is being
> handled as per the alias style example configuration and works well for
> delivering mail to local popboxes. I have a need however to deliver SOME
> emails for a domain to local popboxes and forward the remainder onto
> another SMTP server
In Exim 3: use two directors, each with
domains = your.customers.domain
The first one is a "localuser" one and catches the ones that are to be
delivered locally. (If you are using local mail boxes that aren't the
same as actual local user names, you need something else, possibly
"aliasfile" with a list of the user names that are to be delivered
locally.) The second one is a "smartuser" one and it receives all the
addresses that are not cautght by the first one, and sends them on to
the customer's machine.
In Exim 4 those would be an "accept" router with the
"check_local_user" option and a "redirect" router.