[Exim] Newbie - sendmail "nullclient" equivalent

I'm just getting started with Exim (4.24) after many years of intending
to....

Initially, I'm looking to replace sendmail on our user SMTP submission
machines before moving on to the central mail hubs (and mail delivery
machines).

These submission machines simply route messages received on to our central
mail hubs using a "nullclient" type sendmail configuration. Submitted
messages are simply queued on receipt and then delivered by a background
"sendmail -q" process.

I've configured Exim to queue on receipt and deliver in the background, and
am using the "smart_route" router to try to simulate sendmail's
"nullclient" behaviour. Ideally, I'd like to be able to use the MX records
in the DNS for my "route_list" hosts but understand that I can't, but can
achieve a similar effect using "hosts_randomize"...

smart_route:
driver = manualroute
domains = !+local_domains
transport = remote_smtp
hosts_randomize
route_list = * sysa.bris.ac.uk:sysb.bris.ac.uk:sysc.bris.ac.uk

This is working well for me with the exception that when the queue of
messages is processed, established SMTP connections are not being reused.
Ideally, I'd like each "exim -q" process to pick one of the route_list
hosts (at random) and send all messages in the queue to it (resuing the
connection it's initially established). Is this possible?

Cheers,

Richard Hopkins,
Information Services,
Computer Centre,
University of Bristol,
Bristol, BS8 1UD, UK

Tel +44 117 928 7859
Fax +44 117 929 1576