The VPOP3 Spamfilter Quarantine is a place where messages may be placed by the VPOP3 spam filter if they are deemed suspicious enough. The VPOP3 spam filter does not just delete messages because all spam filters have the risk of 'false positives' where legitimate messages are incorrectly detected as spam.
Each VPOP3 user has their own quarantine area where there suspicious messages are stored. Non-user entities (such as lists or forwarding email addresses) do not have a quarantine area so suspicious messages to those cannot be placed into a quarantine for that entity.
VPOP3 will hold the messages in the quarantine for a set time (default 14 days) and then automatically delete them. This time can be configured in the Quarantine Settings.
Every day, VPOP3 will send a message to each user who has at least one message placed into the quarantine. This message will contain a summary of the quarantined messages, along with a link which can be used to view the message (and optionally release it for delivery). It is possible to alter the time when this summary message is generated, and even set VPOP3 to generate more than one a day. Again, this is set in the Quarantine Settings.
Users can access their own quarantined messages at any time by logging into their Webmail account and selecting the 'Quarantine' tab.
Administrators can access the quarantined messages for any user by going to the Settings -> Spamfilter -> Quarantine Viewer page.
It is possible to disable the quarantine either globally (in Settings -> Spamfilter -> General -> Quarantine settings) or for an individual user (in Edit User -> Advanced). In this case, suspicious messages will be delivered to the user instead of placed into the quarantine.