[Exim] System wide filter

Hi,
I am trying to set up a system wide filter on a Exim 3.16 running on Digital
Alpha. Chpt 44 of the documentation luckily has an example transport which
seems to do what I want. I have a couple of questions to ask before I deploy the
new conf file though as I don't have a test system to play with first.
Here's the example transport:

central_filter:
driver = forwardfile
file = /path/to/file/${local_part}
no_check_local_user
no_verify
filter
allow_system_actions

At my site there are about 50 users. I only want to create filters for some users
on a per need-to-basis. I need to be able to centrally manage the filters for
individual users. This might also include vacation filters.

Question 1) My understanding of this transport is that it will search for a file to
match the local part of the recipient. It a file exists (in the path given) it will
apply the filter if not it will continue as a normal delivery. Is that correct?

Question 2) According to the docs this allows me to use the ${local_part} (and
$domain) variables, so I could theoretically limit email sizes for some users, with
a filter such as; if ${local_part} contains "heavyuser" and $message_size is not
below 4000 then fail text "Message to large for this user". Does that seems right?

Question 3) I already have a sender_reject_recipients in the conf file. Will the
no_check_local_user or no_verify interfere with this. I still need to halt mail from
one or two hosts (spammers), which I guess I can do with the central filter after
but I do like sender_reject.

Question 4) Has anyone else successfully set a system wide filter which would do
what I am after? If so could I have a look :-), I would like to see if the example is
very different from what I am about to embark on.

Thanx for taking the time.
Dp.


~~
Dermot Paikkos * dermot@???
Network Administrator @ Science Photo Library
Phone: 0207 432 1100 * Fax: 0207 286 8668