This was the reply from my friend, Dan Shearer:
You want to do what?!? <snip>
You want to send a copy of all email being delivered on a server to a
single address on a particular remote server. A very blind and stupid
archive system (that won't do anything sensible with expansions and
multiple copies and whatnot) but also a reliable one.
I suggest that:
1. You can do everything you want in an Exim filter, and
2. You will like filters much more than Exim configs
Therefore, I propose you solve your problem with a global filter (you
can also have a filter file per-user.)
A filter file is slightly harder than a .forward file and easier than
procmail.
You start with this in the Exim config file:
system_filter = /etc/exim4/exim4.filter
I'm pretty sure you want just one single line in your filter to solve
the whole problem (it's like a global .forward):
unseen deliver myaddress@???
I suspect you might want to add this before the deliver command:
headers add "Archive copy from branch"
You can test a filter from the commandline:
exim -bF filter < amessage
You hopefully won't need it, but see also:
http://exim.org/exim-html-current/doc/html/filter.html#
And
http://www.exim.org/exim-html-current/doc/html/spec_html/ch43.html