Sending Spam to a Quarantine
SpamAssassin itself just tags the messages it scans as spam or nonspam; if you want to quarantine spam, you will need an add-on product that does this. Here's a list (please expand it if you know of more!)
http://www.renaissoft.com/maia/ : Maia Mailguard is 'a web-based interface and management system for the popular amavisd-new e-mail scanner and SpamAssassin. Written in Perl and PHP, Maia Mailguard gives end-users control over how their mail is processed by virus scanners and spam filters, while giving mail administrators the power to configure site-wide defaults and limits.'
http://www.biodef.org/SpamAssassin/Quarantine/ or http://sourceforge.net/projects/saq : 'SAQ is a SpamAssassin Quarantine system that picks potential Spam emails out of the mailstream and puts them aside. Recipients receive daily reports about quarantined emails with a link to click on if they wish to recive any particular email in their inbox.'