[Exim] Authenticated SMTP on port 587

Hi All,

I'm currently running Exim 4.31, and I want to run a separate instance of
Exim on the submission port (587) that allows authenticated SMTP only. This
instance of Exim would then deliver the message via remote SMTP or locally
(either by SMTP or by inserting it into the queue).

So far, I have this running by starting this separate instance of Exim with:
exim -bd -oX 587 -C configure.587

In this separate configuration, I only accept authenticated SMTP connection
with something like:

check_recipient:
  accept  hosts = +auth_relay_hosts
          endpass
          message = relay not permitted, authentication required
          authenticated = *
  deny    message = relay not permitted

However, this is where I get a bit stuck - how do I set up the relevant
router & transport to handle the accepted message? I assume I only need a
remote_smtp type setup, but will this be able to take account of local mail
deliveries?

Many, many thanks in advance :)

--Alex