I use ASSP in the front of Zimbra with great success. The users reports spams by forwarding the e-mail to spam@assp.local or nospam@assp.local.
But I was thinking if there is a way to turn this more easy:

Maybe a Sieve filter that when the message arrive to the SPAM folder (by pressing the spam button), it will be automatically forwarded to assp@assp.local.
To report non-spam, I think that we haven't a way to revert the proccess, but ok.