[exim] Meta: Debian and Exim

I don't know anything about the way Debian pakages Exim for distribution.
(Actually, that's not true - I know that some versions of Debian persist a
version of Exim 3, which is upgradeable by the user if they know how, and
also that sometimes the config file is split into fragments which are
rebuilt on the fly).

An increasing number of questions are posted here by newbie users of Exim,
who got the software with their Debian distro and need help with it. I,
along with, I suspect, many others here, am unable to help them in anything
more than general terms because of my lack of knowledge of how the Debian
package hangs together.

Is there a resource somewhere which describes in terms I would understand
how the Debian distribution of Exim 4 differs from the standard vanilla
distribution? If there is, I'd gladly go learn about it in order to be more
helpful to this particular community of Exim users. I don't have the time to
get steeped in all things Debian, though.

The same question applies to Cpanel + Exim, from which I run a mile becuase
I've seen some of the messes that Cpanel users get themselves in when they
make seemingly simple Exim config changes.

Any advice welcome.

Peter