[Exim] Routing mail via "smarthost" with only MX records.

Our campus is set up so that all incoming and outgoing mail has to be routed
via the campus mail servers. For incoming mail this is not a problem as it
gets passed on to our mail server.

However, I'm having trouble getting Exim to route outgoing messages via the
mail servers as the mail server DNS entry only has MX records. AFAIK this
should be perfectly fine and has worked for years with sendmail, and it's
not something which I can change.

Exim refuses to route the mail as the smtp transport only appears to do a
DNS A record search and no MX record search. I've tried the following two
methods and both fail in the smtp transport with failed lookups on
lepp.le.ac.uk :

   dnslookup:
     driver = manualroute
     domains = ! +local_domains
     transport = remote_smtp
     ignore_target_hosts = 0.0.0.0 : 127.0.0.0/8
     route_list = * lepp.le.ac.uk
     no_more

   remote_smtp:
     driver = smtp

and this pair:

   dnslookup:
     driver = dnslookup
     domains = ! +local_domains
     transport = remote_smtp
     ignore_target_hosts = 0.0.0.0 : 127.0.0.0/8
     no_more

   remote_smtp:
     driver = smtp
     hosts = lepp.le.ac.uk
     hosts_override

Does anyone know how I can get the smtp transport to lookup the MX record
for our campus mail servers?

--
Nigel Wade, System Administrator, Space Plasma Physics Group,
             University of Leicester, Leicester, LE1 7RH, UK
E-mail :    nmw@???
Phone :     +44 (0)116 2523548, Fax : +44 (0)116 2523555