[Exim] HELP: Individual blacklists for each user

Hi

We run a webmail server (with ~16,000 accounts now) - and want to set up server
side blacklists for all our users so that they can killfile anyone (or
anything) they don't want to receive mail from - without blocking them
system-wide. Any pointers would be appreciated ;)

The server is a redhat 6.2 box running Exim 3.13, fwiw.

--
Suresh Ramasubramanian + sureshr@???
Linux is like a Teepee - No Windows, No Gates, Apache Inside