Exim and Spamassasin: few questions

Hi all,

I have Exim4 set on Debian Sarge and now I'd like to add spam protection
with Spamassasin. Users are getting their mail via pop.

Functionally, I'd like all messages marked as spam to be forwarded to
one account, where an employee could review them manually, forward good
messages to 'notspam@' account that would add them to a whitelist and
then resend to the final recipient.
Additionally, I'd like to have 'spam@' address, where users could
forward bad messages not marked as spam by the system and thus improve
the the learning process.

How can this be achieved?
Thanks for any hints.

-marek