[exim] Confusing config format

Hi all, I've recently had to look into an Exim4 configuration on an
Ubuntu system, which was installed using the apt-get method.

This seems to have the config split over a large number of small files,
in many different directories.

There seems to be one file called update-exim4.conf.conf, and then a
conf.d directory will all the other bits in.

How can I convert this into a single (normal!) config file? The other
systems I use are where exim has been manually compiled and installed
have a nice simple, single, config file. This 'exploded' config just
seems (to me, anyway) a massively complicated way of doing things, with
a much greater risk of something somewhere going wrong.

The config files have things like 'domainlist local_domains =
MAIN_LOCAL_DOMAINS' and 'relay_from_hosts = MAIN_RELAY_NETS' in them,
yet I can't find where MAIN_LOCAL_DOMAINS or MAIN_RELAY_NETS is defined.
there is an exntry of dc_relay_nets='[ip]' in update-exim4.conf.conf,
but I don't see how this is converted into the MAIN_RELAY_NETS part.

Please tell me there is way to stop this madness and get back to a
single config file!