Per user Quarantine Area
A spam proxy filter should have some sort of per user quarantine area capabilities each individual employee can manage. So rather than an administrator releasing false positives every day; individual users can manage email destined to them and release their own emails if needed. This is a massive burden off the administrator’s shoulders.
So this feature enables the ability for an end user to see his or her spam email which has been quarantined. They can then release these emails if they wish to do so. Also spam filters have the option where if the spam email is released then the sender would be placed in a whitelist for that user, so per user whitelisting. This will mean future emails from the sender to that particular user will only be scanned for viruses and not scanned for spam.
Wikipedia's guide to Anti Spam Techniques